this is such a wierd bug, seems, as GI says, that if you wait a little while before trying again it works...
still, driving me insane - i'll try lowering my graphics settings and see if it makes any difference
EDIT: i tried lowering the graphics settings to no effect, but then i lowered the refresh rate to 60Hz and it hasnt failed to alt+tab once!
now i think about it, i've gotten a new monitor since i last ran OpFP, and my old one couldnt handle 75Hz so i used to run it at 60...
anyway, it seems to be working now - anyone else like to try it and post their results? ;D