I've reported this to MathWorks and Contexts, but would like to do some additional diagnosis to help them figure this out so the problem can actually be fixed. (Right now, the workaround is "don't run Contexts".)
I tried to use
dtruss to see what Matlab is doing when it hangs, but that causes Matlab to run the Program Activation tool instead of regular Matlab.
Any other ideas on how to diagnose this, or what might be causing it?