I actually used to have an issue when BF3 came out where as Assault if i pressed my 2 key it would pull out my Paddles, yet as engineer if i pressed 2 for repair tool, it wouldn't bring it out or anything for some reason, cause they are the equivalent of each other.
It turned out too be a key binding issue, where my 2 key was binded to Gadget 3 or 4 or w.e it is, but it also needed to be binded to the under slung weapon key binding, when i fiddled around with that it worked fine.
Was a pretty random problem, and sorry if i'm a bit vague on my issue but i can't really remember it in detail.
Basically just change your key bindings around until they work for all classes.
Mind you this was a issue they had patched so might not be an issue anymore, but still best to check it out.
Posted on Friday, 13th January 2012