This is a regression in JDK 1.8.0 update 40.

When an interface method is invoked on a class, "IllegalArgumentException: Not a default method" exception is thrown:
Exception in thread "event-handler" java.lang.IllegalArgumentException: Not a default method
	at com.sun.tools.jdi.ObjectReferenceImpl.validateIfaceMethodInvocation(ObjectReferenceImpl.java:352)
	at com.sun.tools.jdi.ObjectReferenceImpl.validateMethodInvocation(ObjectReferenceImpl.java:292)
	at com.sun.tools.jdi.ObjectReferenceImpl.invokeMethod(ObjectReferenceImpl.java:405)
	at notadefaultmethod.EventThread.testMethodInvoke(EventThread.java:361)
The attached project can be used to reproduce the defect.
Method invocation proceeds without any problems on JDK 1.8.0 update 31. It fails just in update 40.
The interface method validation is problematic.