Steps to reproduce:

• process with non interrupting event suprocess with message start event
• synchronous service task in the main flow which triggers the message event using api

=> Excecption

Notes:
1) The problem is that when the event suprocess is executed, the execution tree is expanded and the scope execution which executed the service task initially is replaced by a new concurrent execution which must be used for leaving the service task. This is not happening, hence the bug.

2) Is it actually in tune with the specification for a process instance to "send itself a message?" - I think not but a) this has to be confirmed and b) we can decide to support it anyway. If we decide against it, a meaningful exception should be thrown when the user attempts to do this.