Oy, sorry to hear that @sparxef, hospital trips are never fun.
I realized at least one thing that is different about the way menu buttons are handled vs in-game world stuff that might be where the game is having trouble. Wont' be able to check until tonight though.
Crazy follow-up question for anyone with this issue: if you happen to have a different mouse available to try out... does switching mice work (different manufacturer)? Or using the trackpad if you're on a laptop? Using any special software for button mapping / customization?