I got a little farther by picking apart the SWC - I think the bugs cease if MainMenu is the only exported class in the SWC, whereas usually there are 20 others. I almost got a hobbled version working, then Flash Builder exploded and fried my workspace and project which I took as a cue to give up on this for now. Filed this as a bug: https://bugs.adobe.com/jira/browse/FB-35844
Wow, this bug made it into the production release. It makes FlashBuilder totally unusable for me because in addition to the profiler hanging, symbols from the SWC are randomly swapped in the output SWF - has noone else experienced this?