Hey this might be late but still, hope I can help:
I was having the same problem as yours, but it was solved when I updated Motion to 5.0.1, I didn’t even see the “Playmode” back in Motion 5.0, maybe it’s a new feature??
Anyway, I’m also running motion on Lion, I think all you need to do is to update Motion.
Cheers
Andy
How soon is now?