I have even rebound it to another key and it still doesn't work.

It works for me. But saves often crashing the game.

what does it mean doesnt work? it wont save? do you get message that quicksave was successful but you can not find the save game? or game crashes?

F5 is default for quicksave check if you didnt change it to something else

 

works fine for me (Steam version) OSX Maverics

In my case, when F5 pressed, game saves, but then it freezes for about 15-20 seconds and then exit to desktop with crash report.

If I launch game again I could load this save.