The EventSet docs state --

  The event that are grouped in an EventSet are restricted in the following ways:

      Always singleton sets:
            VMStartEvent
            VMDeathEvent
            VMDisconnectEvent
      Only with other ThreadStartEvents for the same thread:
            ThreadStartEvent
      Only with other ThreadDeathEvents for the same thread:
            ThreadDeathEvent
      Only with other ClassPrepareEvents for the same class:
            ClassPrepareEvent
      Only with other ClassUnloadEvents for the same class:
            ClassUnloadEvent
      Only with other AccessWatchpointEvents for the same field access:
            AccessWatchpointEvent
      Only with other ModificationWatchpointEvents for the same field modification:
            ModificationWatchpointEvent
      Only with other ExceptionEvents for the same exception occurrance:
            ExceptionEvent
      Only with other members of this group, at the same location and in the same thread:
            BreakpointEvent
            StepEvent
            MethodEntryEvent
            MethodExitEvent

The last of these is wrong and should be --

      Only with other MethodExitEvent for the same method exit:
            MethodExitEvent
      Only with other members of this group, at the same location and in the same thread:
            BreakpointEvent
            StepEvent
            MethodEntryEvent