FULL PRODUCT VERSION :
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Darwin my-mbp 14.1.0 Darwin Kernel Version 14.1.0: Thu Feb 26 19:26:47 PST 2015; root:xnu-2782.10.73~1/RELEASE_X86_64 x86_64

A DESCRIPTION OF THE PROBLEM :
Nashorn is causing keys on an object to become undefined when an object with more than 256 keys and where the keys are themselves objects.

e.g. objects of the form:
var foo = {
    field_1: { code: 1 },
    field_2: { code: 2 },
    ...
    field_256: { code: 256 }
}

Where when enumerating up to field_257 in the same form will cause all fields foo.field_<i> to become undefined. When enumerating only up to field_256, all fields contain the expected value.

The problem only occurs when the values are also objects, so objects of the form:

var bar = {
    field_1: 1,
    field_2: 2,
    ...
    field_256: 256
}

appear to be unaffected.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Running:
jjs map_256.js

emits: foo, # of keys= 256 first field= [object Object]

Running:
jjs map_257.js

emits: foo, # of keys= 257 first field= undefined

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expect map_257.js to print:
foo, # of keys= 257 first field= [object Object]

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
map_256.js:
var foo = {
field_1: { code: "1" },
field_2: { code: "2" },
field_3: { code: "3" },
field_4: { code: "4" },
field_5: { code: "5" },
field_6: { code: "6" },
field_7: { code: "7" },
field_8: { code: "8" },
field_9: { code: "9" },
field_10: { code: "10" },
field_11: { code: "11" },
field_12: { code: "12" },
field_13: { code: "13" },
field_14: { code: "14" },
field_15: { code: "15" },
field_16: { code: "16" },
field_17: { code: "17" },
field_18: { code: "18" },
field_19: { code: "19" },
field_20: { code: "20" },
field_21: { code: "21" },
field_22: { code: "22" },
field_23: { code: "23" },
field_24: { code: "24" },
field_25: { code: "25" },
field_26: { code: "26" },
field_27: { code: "27" },
field_28: { code: "28" },
field_29: { code: "29" },
field_30: { code: "30" },
field_31: { code: "31" },
field_32: { code: "32" },
field_33: { code: "33" },
field_34: { code: "34" },
field_35: { code: "35" },
field_36: { code: "36" },
field_37: { code: "37" },
field_38: { code: "38" },
field_39: { code: "39" },
field_40: { code: "40" },
field_41: { code: "41" },
field_42: { code: "42" },
field_43: { code: "43" },
field_44: { code: "44" },
field_45: { code: "45" },
field_46: { code: "46" },
field_47: { code: "47" },
field_48: { code: "48" },
field_49: { code: "49" },
field_50: { code: "50" },
field_51: { code: "51" },
field_52: { code: "52" },
field_53: { code: "53" },
field_54: { code: "54" },
field_55: { code: "55" },
field_56: { code: "56" },
field_57: { code: "57" },
field_58: { code: "58" },
field_59: { code: "59" },
field_60: { code: "60" },
field_61: { code: "61" },
field_62: { code: "62" },
field_63: { code: "63" },
field_64: { code: "64" },
field_65: { code: "65" },
field_66: { code: "66" },
field_67: { code: "67" },
field_68: { code: "68" },
field_69: { code: "69" },
field_70: { code: "70" },
field_71: { code: "71" },
field_72: { code: "72" },
field_73: { code: "73" },
field_74: { code: "74" },
field_75: { code: "75" },
field_76: { code: "76" },
field_77: { code: "77" },
field_78: { code: "78" },
field_79: { code: "79" },
field_80: { code: "80" },
field_81: { code: "81" },
field_82: { code: "82" },
field_83: { code: "83" },
field_84: { code: "84" },
field_85: { code: "85" },
field_86: { code: "86" },
field_87: { code: "87" },
field_88: { code: "88" },
field_89: { code: "89" },
field_90: { code: "90" },
field_91: { code: "91" },
field_92: { code: "92" },
field_93: { code: "93" },
field_94: { code: "94" },
field_95: { code: "95" },
field_96: { code: "96" },
field_97: { code: "97" },
field_98: { code: "98" },
field_99: { code: "99" },
field_100: { code: "100" },
field_101: { code: "101" },
field_102: { code: "102" },
field_103: { code: "103" },
field_104: { code: "104" },
field_105: { code: "105" },
field_106: { code: "106" },
field_107: { code: "107" },
field_108: { code: "108" },
field_109: { code: "109" },
field_110: { code: "110" },
field_111: { code: "111" },
field_112: { code: "112" },
field_113: { code: "113" },
field_114: { code: "114" },
field_115: { code: "115" },
field_116: { code: "116" },
field_117: { code: "117" },
field_118: { code: "118" },
field_119: { code: "119" },
field_120: { code: "120" },
field_121: { code: "121" },
field_122: { code: "122" },
field_123: { code: "123" },
field_124: { code: "124" },
field_125: { code: "125" },
field_126: { code: "126" },
field_127: { code: "127" },
field_128: { code: "128" },
field_129: { code: "129" },
field_130: { code: "130" },
field_131: { code: "131" },
field_132: { code: "132" },
field_133: { code: "133" },
field_134: { code: "134" },
field_135: { code: "135" },
field_136: { code: "136" },
field_137: { code: "137" },
field_138: { code: "138" },
field_139: { code: "139" },
field_140: { code: "140" },
field_141: { code: "141" },
field_142: { code: "142" },
field_143: { code: "143" },
field_144: { code: "144" },
field_145: { code: "145" },
field_146: { code: "146" },
field_147: { code: "147" },
field_148: { code: "148" },
field_149: { code: "149" },
field_150: { code: "150" },
field_151: { code: "151" },
field_152: { code: "152" },
field_153: { code: "153" },
field_154: { code: "154" },
field_155: { code: "155" },
field_156: { code: "156" },
field_157: { code: "157" },
field_158: { code: "158" },
field_159: { code: "159" },
field_160: { code: "160" },
field_161: { code: "161" },
field_162: { code: "162" },
field_163: { code: "163" },
field_164: { code: "164" },
field_165: { code: "165" },
field_166: { code: "166" },
field_167: { code: "167" },
field_168: { code: "168" },
field_169: { code: "169" },
field_170: { code: "170" },
field_171: { code: "171" },
field_172: { code: "172" },
field_173: { code: "173" },
field_174: { code: "174" },
field_175: { code: "175" },
field_176: { code: "176" },
field_177: { code: "177" },
field_178: { code: "178" },
field_179: { code: "179" },
field_180: { code: "180" },
field_181: { code: "181" },
field_182: { code: "182" },
field_183: { code: "183" },
field_184: { code: "184" },
field_185: { code: "185" },
field_186: { code: "186" },
field_187: { code: "187" },
field_188: { code: "188" },
field_189: { code: "189" },
field_190: { code: "190" },
field_191: { code: "191" },
field_192: { code: "192" },
field_193: { code: "193" },
field_194: { code: "194" },
field_195: { code: "195" },
field_196: { code: "196" },
field_197: { code: "197" },
field_198: { code: "198" },
field_199: { code: "199" },
field_200: { code: "200" },
field_201: { code: "201" },
field_202: { code: "202" },
field_203: { code: "203" },
field_204: { code: "204" },
field_205: { code: "205" },
field_206: { code: "206" },
field_207: { code: "207" },
field_208: { code: "208" },
field_209: { code: "209" },
field_210: { code: "210" },
field_211: { code: "211" },
field_212: { code: "212" },
field_213: { code: "213" },
field_214: { code: "214" },
field_215: { code: "215" },
field_216: { code: "216" },
field_217: { code: "217" },
field_218: { code: "218" },
field_219: { code: "219" },
field_220: { code: "220" },
field_221: { code: "221" },
field_222: { code: "222" },
field_223: { code: "223" },
field_224: { code: "224" },
field_225: { code: "225" },
field_226: { code: "226" },
field_227: { code: "227" },
field_228: { code: "228" },
field_229: { code: "229" },
field_230: { code: "230" },
field_231: { code: "231" },
field_232: { code: "232" },
field_233: { code: "233" },
field_234: { code: "234" },
field_235: { code: "235" },
field_236: { code: "236" },
field_237: { code: "237" },
field_238: { code: "238" },
field_239: { code: "239" },
field_240: { code: "240" },
field_241: { code: "241" },
field_242: { code: "242" },
field_243: { code: "243" },
field_244: { code: "244" },
field_245: { code: "245" },
field_246: { code: "246" },
field_247: { code: "247" },
field_248: { code: "248" },
field_249: { code: "249" },
field_250: { code: "250" },
field_251: { code: "251" },
field_252: { code: "252" },
field_253: { code: "253" },
field_254: { code: "254" },
field_255: { code: "255" },
field_256: { code: "256" }
};

print("foo, # of keys=", Object.keys(foo).length, "first field=", foo.field_1);

===================================
map_257.js
var foo = {
field_1: { code: "1" },
field_2: { code: "2" },
field_3: { code: "3" },
field_4: { code: "4" },
field_5: { code: "5" },
field_6: { code: "6" },
field_7: { code: "7" },
field_8: { code: "8" },
field_9: { code: "9" },
field_10: { code: "10" },
field_11: { code: "11" },
field_12: { code: "12" },
field_13: { code: "13" },
field_14: { code: "14" },
field_15: { code: "15" },
field_16: { code: "16" },
field_17: { code: "17" },
field_18: { code: "18" },
field_19: { code: "19" },
field_20: { code: "20" },
field_21: { code: "21" },
field_22: { code: "22" },
field_23: { code: "23" },
field_24: { code: "24" },
field_25: { code: "25" },
field_26: { code: "26" },
field_27: { code: "27" },
field_28: { code: "28" },
field_29: { code: "29" },
field_30: { code: "30" },
field_31: { code: "31" },
field_32: { code: "32" },
field_33: { code: "33" },
field_34: { code: "34" },
field_35: { code: "35" },
field_36: { code: "36" },
field_37: { code: "37" },
field_38: { code: "38" },
field_39: { code: "39" },
field_40: { code: "40" },
field_41: { code: "41" },
field_42: { code: "42" },
field_43: { code: "43" },
field_44: { code: "44" },
field_45: { code: "45" },
field_46: { code: "46" },
field_47: { code: "47" },
field_48: { code: "48" },
field_49: { code: "49" },
field_50: { code: "50" },
field_51: { code: "51" },
field_52: { code: "52" },
field_53: { code: "53" },
field_54: { code: "54" },
field_55: { code: "55" },
field_56: { code: "56" },
field_57: { code: "57" },
field_58: { code: "58" },
field_59: { code: "59" },
field_60: { code: "60" },
field_61: { code: "61" },
field_62: { code: "62" },
field_63: { code: "63" },
field_64: { code: "64" },
field_65: { code: "65" },
field_66: { code: "66" },
field_67: { code: "67" },
field_68: { code: "68" },
field_69: { code: "69" },
field_70: { code: "70" },
field_71: { code: "71" },
field_72: { code: "72" },
field_73: { code: "73" },
field_74: { code: "74" },
field_75: { code: "75" },
field_76: { code: "76" },
field_77: { code: "77" },
field_78: { code: "78" },
field_79: { code: "79" },
field_80: { code: "80" },
field_81: { code: "81" },
field_82: { code: "82" },
field_83: { code: "83" },
field_84: { code: "84" },
field_85: { code: "85" },
field_86: { code: "86" },
field_87: { code: "87" },
field_88: { code: "88" },
field_89: { code: "89" },
field_90: { code: "90" },
field_91: { code: "91" },
field_92: { code: "92" },
field_93: { code: "93" },
field_94: { code: "94" },
field_95: { code: "95" },
field_96: { code: "96" },
field_97: { code: "97" },
field_98: { code: "98" },
field_99: { code: "99" },
field_100: { code: "100" },
field_101: { code: "101" },
field_102: { code: "102" },
field_103: { code: "103" },
field_104: { code: "104" },
field_105: { code: "105" },
field_106: { code: "106" },
field_107: { code: "107" },
field_108: { code: "108" },
field_109: { code: "109" },
field_110: { code: "110" },
field_111: { code: "111" },
field_112: { code: "112" },
field_113: { code: "113" },
field_114: { code: "114" },
field_115: { code: "115" },
field_116: { code: "116" },
field_117: { code: "117" },
field_118: { code: "118" },
field_119: { code: "119" },
field_120: { code: "120" },
field_121: { code: "121" },
field_122: { code: "122" },
field_123: { code: "123" },
field_124: { code: "124" },
field_125: { code: "125" },
field_126: { code: "126" },
field_127: { code: "127" },
field_128: { code: "128" },
field_129: { code: "129" },
field_130: { code: "130" },
field_131: { code: "131" },
field_132: { code: "132" },
field_133: { code: "133" },
field_134: { code: "134" },
field_135: { code: "135" },
field_136: { code: "136" },
field_137: { code: "137" },
field_138: { code: "138" },
field_139: { code: "139" },
field_140: { code: "140" },
field_141: { code: "141" },
field_142: { code: "142" },
field_143: { code: "143" },
field_144: { code: "144" },
field_145: { code: "145" },
field_146: { code: "146" },
field_147: { code: "147" },
field_148: { code: "148" },
field_149: { code: "149" },
field_150: { code: "150" },
field_151: { code: "151" },
field_152: { code: "152" },
field_153: { code: "153" },
field_154: { code: "154" },
field_155: { code: "155" },
field_156: { code: "156" },
field_157: { code: "157" },
field_158: { code: "158" },
field_159: { code: "159" },
field_160: { code: "160" },
field_161: { code: "161" },
field_162: { code: "162" },
field_163: { code: "163" },
field_164: { code: "164" },
field_165: { code: "165" },
field_166: { code: "166" },
field_167: { code: "167" },
field_168: { code: "168" },
field_169: { code: "169" },
field_170: { code: "170" },
field_171: { code: "171" },
field_172: { code: "172" },
field_173: { code: "173" },
field_174: { code: "174" },
field_175: { code: "175" },
field_176: { code: "176" },
field_177: { code: "177" },
field_178: { code: "178" },
field_179: { code: "179" },
field_180: { code: "180" },
field_181: { code: "181" },
field_182: { code: "182" },
field_183: { code: "183" },
field_184: { code: "184" },
field_185: { code: "185" },
field_186: { code: "186" },
field_187: { code: "187" },
field_188: { code: "188" },
field_189: { code: "189" },
field_190: { code: "190" },
field_191: { code: "191" },
field_192: { code: "192" },
field_193: { code: "193" },
field_194: { code: "194" },
field_195: { code: "195" },
field_196: { code: "196" },
field_197: { code: "197" },
field_198: { code: "198" },
field_199: { code: "199" },
field_200: { code: "200" },
field_201: { code: "201" },
field_202: { code: "202" },
field_203: { code: "203" },
field_204: { code: "204" },
field_205: { code: "205" },
field_206: { code: "206" },
field_207: { code: "207" },
field_208: { code: "208" },
field_209: { code: "209" },
field_210: { code: "210" },
field_211: { code: "211" },
field_212: { code: "212" },
field_213: { code: "213" },
field_214: { code: "214" },
field_215: { code: "215" },
field_216: { code: "216" },
field_217: { code: "217" },
field_218: { code: "218" },
field_219: { code: "219" },
field_220: { code: "220" },
field_221: { code: "221" },
field_222: { code: "222" },
field_223: { code: "223" },
field_224: { code: "224" },
field_225: { code: "225" },
field_226: { code: "226" },
field_227: { code: "227" },
field_228: { code: "228" },
field_229: { code: "229" },
field_230: { code: "230" },
field_231: { code: "231" },
field_232: { code: "232" },
field_233: { code: "233" },
field_234: { code: "234" },
field_235: { code: "235" },
field_236: { code: "236" },
field_237: { code: "237" },
field_238: { code: "238" },
field_239: { code: "239" },
field_240: { code: "240" },
field_241: { code: "241" },
field_242: { code: "242" },
field_243: { code: "243" },
field_244: { code: "244" },
field_245: { code: "245" },
field_246: { code: "246" },
field_247: { code: "247" },
field_248: { code: "248" },
field_249: { code: "249" },
field_250: { code: "250" },
field_251: { code: "251" },
field_252: { code: "252" },
field_253: { code: "253" },
field_254: { code: "254" },
field_255: { code: "255" },
field_256: { code: "256" },
field_257: { code: "257" }
};

print("foo, # of keys=", Object.keys(foo).length, "first field=", foo.field_1);

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None known.