For example, test/com/sun/jdi/PopAndStepTest.java fails like this:
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:452)
at java.util.AbstractList$Itr.hasNext(AbstractList.java:418)
at com.sun.tools.jdi.ThreadReferenceImpl.processThreadAction(ThreadReferenceImpl.java:489)
at com.sun.tools.jdi.ThreadReferenceImpl.sendResumingCommand(ThreadReferenceImpl.java:94)
at com.sun.tools.jdi.StackFrameImpl.pop(StackFrameImpl.java:313)
at com.sun.tools.jdi.ThreadReferenceImpl.popFrames(ThreadReferenceImpl.java:450)
at PopAndStepTest.runOnce(PopAndStepTest.java:137)
at PopAndStepTest.runTests(PopAndStepTest.java:107)
at TestScaffold.startTests(TestScaffold.java:396)
at PopAndStepTest.main(PopAndStepTest.java:56)

This starts happening with TL autobuild 039b in which the fix
for 4902078 was introduced. Several other JPDA jtreg tests
fail as well as many NSK JPDA tests.

No changes have been made to the JDI code in this area, and
preliminary analysis indicates that the JDI code isn't doing anything
wrong.