When a ScopeImpl that is already shared is dupUnshared, the result is a ScopeImpl that partly contains and partly does not contain any Symbols added in the child Scopes. Moreover "remove" crashes with a NPE:
java.lang.NullPointerException
at com.sun.tools.javac.code.Scope$ScopeImpl.remove(Scope.java:406)
at DupUnsharedTest.run(DupUnsharedTest.java:72)
at DupUnsharedTest.main(DupUnsharedTest.java:37)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.sun.javatest.regtest.MainWrapper$MainThread.run(MainWrapper.java:94)
at java.lang.Thread.run(Thread.java:745)

Test case is attached.