Most of the roundtrip scenarios i.e. Java > Js > Java fails to work with new Plug-in but it's working fine with old plug-in.
1) It fails to work when called within the start() or init() method of an applet. It works fine once applet is started
2) This regression got introduced in 6u18-b03

Steps to reproduce:
--------------------
1)Try to load any of the following applet
if TEST PASSED is not getting printed on the Java console then bug is reproduced
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/JSObjectSetMemberCrash.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/JSObjectSetMember.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/RoundTripUserDefined.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/RoundTripJSWin.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/RoundTripUDGetMember.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/RoundTripDiffApplets.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/JSObectOvrloadStr.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/JSObectOvrload.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/DynamicAppletTest.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/RoundTripModalEDT.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/TestJavaArray.html
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/LiveConnect/LiveConnect/html/auto/JSJavaJS.html

These tests points to following inside the automated testabse which will end up as "FAILED" inside the report due to this bug:
test.case.name=SetMemberTest
test.case.name=SetMemberCrashTest
test.case.name=RoundTripUserDefTest
test.case.name=RoundTripJSWinTest
test.case.name=RoundTripUDGetMember
test.case.name=RoundTripAppletComm
test.case.name=JSObjectOvrldTest
test.case.name=JSObjectOvrldStrTest
test.case.name=DynamicAppletTest
test.case.name=RoundTripModalEDTGUI
test.case.name=ArrayDirectTest
test.case.name=JStoJavaToJ