http://bugs.winehq.org/show_bug.cgi?id=33467
--- Comment #9 from Ken Thomases ken@codeweavers.com 2013-04-28 20:57:19 CDT --- Oh, I should also note for posterity that this only affects full-screen games running at full resolution. If the game switches resolution, then the displays are captured and Command-Tab behaves differently. When the displays are captured, the OS doesn't handle Command-Tab. The keystroke is received by the Mac driver, which releases the capture and hides itself (roughly as a means of switching to the next app).
Because of this, you can access your other apps just fine.
When you switch back to the Wine process, it shows but doesn't automatically recapture the display nor change the resolution back. Ideally, the Windows game should do that, but not all do. So, it often ends up showing in just a corner of the screen with the Mac menu bar and Dock visible. Some day I may make the Mac driver recapture the displays and restore the game's chosen resolution.