This issue was reported in B629 and still remains in B649: http://isiforums.net/f/showthread.php/19184-Unstable-629?p=263792&viewfull=1#post263792 I'm guessing the keyboard shortcut Alt/M should be removed now that there's a proper player file entry for the setting? Fyi, my player file is not write protected.
Just did a quick test with build 660 and it seems ok now. I'll report back if I manage to get it to happen again.
Yep! It seems, it happpen , if you do the alt/tab 2-3 times. Sometimes it doesn`t happen after one time tabbing.