I've been having issues with the Steam Overlay while playing The Witcher recently. I suspect that the issues are specific to the fact that the game was (somewhat sloppily) ported to Mac OS X with a quick Wineskin wrapper - a theory supported by this question. Specifically, the Overlay appears when I hit Shift-Tab (most of the time. Sometimes it's totally non-responsive until I restart the game), but it's completely non-interactive. The cursor remains as the games custom cursor, and I can still interact with the game behind the overlay. I cannot however, click on anything on the overlay.
Is there anything I can do to fix the overlay to make it usable?