I never heard about such issue.
Do you have any errors in error log that might indicate a cause ?
Nothing verbose. I went so far as to launch PDE, but there was sort of an emergency so I had to move on. The workaround I went with was to install the standalone JBoss Dev Studio.
For plugin development's sake, I'm sure I'll be able to reproduce by reverting my installation to the known fail-case.
For what it's worth:
The project-level context menu was killed. However, I could use all the options that would have been available by selecting the project and using either the menu bar or my hud.
I could not launch project properties this way, though. So my suspicion is that some error or conflict in the properties triggered the behavior.
Also, this was reproduced in a clean workspace.