A hint to other users: as far as I can tell, F11 and F12 can't be reassigned. When I first tried reassignment, I was hugely frustrated...but only because I was trying to reassign those two keys for functions within Word. F1 through F10 work fine.
I'm new here; I guess what I had to say is in the subject line....
(After all the frustration of not being able to use F-keys the way I'm used to, it was wonderful to discover that the problem could be bypassed.
MacBook Pro, Mac OS X (10.7.5), For working within Word