Control-F2 "Move Focus to Menu Bar" only works occasionally

I don't want to use my trackpad too much due to a strain injury, hence I use the Control F2 "Move Focus to Menu Bar" a lot. However this feature only works occasionally, it can work for hours and then suddenly stop working, sometimes I can fix in the Keyboard Shortcuts pref pane by unchecking and checking the "Move Focus to Menu Bar" checkbox, at other times it takes a restart of the system. I'm a big Apple fan-boy, and I always marvel at the cool features in OSX, this is the first time I have a Windows-esque experience with the OSX UI :(