Description of problem: See linked issue.
This is similar to Bug 1005205: These types of event definitions are only valid if the Start Event is contained in a SubProcess. See table 10.85 of the BPMN 2.0 specification. The fact that you can add these event definitions from the toolpalette is a bug.
Verified on BPMN2 Editor 0.2.7.201309191900 (JBTIS 4.1.3.Beta3)
This BZ has been part of the 6.0.0 stream.