In fact, on some distros it seem C::B have problems with SHIFT+Fxx, CTRL+Fxx and stuff like that.
I should say that Xorg have problems, because the problem is not a C::B only one...
I have tried to find how to solve that problem by myself (on Debian) but I failed (but I did not asked on forums or IRC so maybe someone there would know the solution).
If you find any clue, please share it. (Note that I am not really experienced with Linux actually and that I do not understand the working of Xorg so you could find a solution that I did not found)