A temporary workaround has been described here:
But this error has to be addressed and is not at the time of this message.
There is also a bug report tracking this on the BPMN2 Editor side:
This should also be reported on the jBPM side.
In version 0.0.1.201209171624 of the BPMN2 Editor the problem has been addressed and fixed. I believe it is a temporary solution but am not sure about that.