For some threads, the JVMDI thread start event is being sent from the wrong thread. The JVMDI specification states that the event hook is always called from the newly started thread. In the case of RunDebugThread and in the case of normal java.lang.Thread.start(), the event is issued from the creating thread instead of the newly created thread. The thread start events appear to be correct only for the initial java "main" thread and for JNI-attached threads.