So, when I try and bind the F key to something different, the new function gets bound to F, but the default function doesn't get UN-bound from the F key. I end up with an F key that does whatever I've told it to in options, PLUS whatever the default function is. As far as I can tell, it's only with the F key, too.

Anybody got any ideas?

I think I ran into the same issue. I couldn't for the life of me figure out why "Cancel bodysnatch" wasn't working on the keys I set it to, so I just starting walking across the keyboard until one of them did something. Turns out it was stuck to F, which is definitely neither of the keys I bound it to.

In my case I use AutoHotKey with a lot of games so I created a script to bind F to my bind, which I set to C. I have no idea how to fix it in-game, and I don't want to try to edit the binary-looking config file that saves your custom binds -
%LOCALAPPDATA%\DH2\Saved\SaveGames\SaveOptions.sav