While the test runs fine in its entirety in both configurations, a subsection of it that I whittled down to reproduce another bug does not.

Consider the script (attached as 'nosuch.js')

function invokeMegamorphic() {
    var o = {};
    var s = String.fromCharCode(97);
    o[s] = 1;
    try {
print(Debug.map(o));
o._();
    } catch (e) {
print(e);
    }
}

Object.prototype.__noSuchProperty__ = function() {
    print("no such property", Array.prototype.slice.call(arguments));
};
invokeMegamorphic();

Object.prototype.__noSuchMethod__ = function() {
    print("no such method", Array.prototype.slice.call(arguments));
};

invokeMegamorphic();

Running it in the default 9 configuration (with -Dnashorn.debug enabled) produces this output:

0x3972a855 = {
['a'@0x62e7f11d (writable enumerable configurable) Accessor type=i slot=0]
}
no such property _
TypeError: Cannot call undefined
0x101952da = {
['a'@0x6babf3bf (writable enumerable configurable) Accessor type=i slot=0]
}
no such method _


... but turning off ot for the same build (running with --optimistic-types=false -Dnashorn.debug) produces

0x424e1977 = {
['a'@0x10d68fcd (writable enumerable configurable) Accessor type=i slot=0]
}
no such property _
TypeError: Cannot call undefined
0x424e1977 = {
['a'@0x10d68fcd (writable enumerable configurable) Accessor type=i slot=0]
}
no such property _
TypeError: Cannot call undefined


The default configuration in 9 is optimistic types enabled. Not that with ot false, we get the same no such property printout twice, instead of the second one being a nosuchmethod. As far as I can tell, the latter is the correct behavior.