After quite a bit of work using the tool, my interaction diagram entered a bad state where it is impossible to add any messages and have them save/display properly.

Specifically, if I add any message and close the diagram all new messages will have their labels and arrow endings missing. When I show properties for these messages the properties editor is for a "Graphics Object" and is titled "Graph Edge true"

Clearly this makes my diagram unusable and is a loss of most/all work that has gone into the diagram, so I suggest this is a critical bug.

Are there any workarounds, patches or plans to fix?

damonfeldman,
I have replied to your post at
http://www.myeclipseide.com/index.php?name=PNphpBB2&file=viewtopic&p=109000#109000