I've been living with this same problem for a while now....
I find that if I alt-tab once, all that happens is I get an additional Windows cursor within mission editor.
If I alt-tab once more, the screen will minimize and pop right back up.
I usually have IE open to the forums with I'm editing anyway, so if I alt-tab a 3rd time, it will switch over to IE and I'm fine.
I can then minimize IE and launch notepad or whatever else I need to do.
Yes, it's a pain in the 6, but I was without OFP for months and now that I have it working properly (somewhat) again, I don't care if I have to dance a jig and paint my face orange - as long as it works!!!!
Try that out and see if it helps....
;D