Steps to reproduce the bug: Go into mouselook mode (either hit "m" or use the mousewheel). Alt-tab to another app. Alt-tab back to SL. Scroll mousewheel to get out of mouselook mode. Note: this is in windowed mode; dunno about full-screen mode.
Observed results: Can't get out of mouselook mode via mousewheel.
Expected results: Alt-tabbing shouldn't affect mousewheel getting out of mouselook mode.