I have been noticing that render region acts weird for me after a couple of iterations, especially with particle fluids. It will render a couple of times, then just not work, and mplayer won't launch either if I try to create a mantra frame render.
Only quitting and restarting Apprentice will fix the issue. Does this sound like an issue with my install or a common problem?

Thanks
Alex

I noticed that as well. Sometimes the renderer proper hangs as well. I set up something to render, come back after a night and it's done *nothing*, so I'll restart the app and it busies away as it should.

I agree too, sometimes it hang on the application because of memory issues.