Do you have Shield Expertise? That should not matter, though, as the extra damage is applied even if you are using a two handed sword. <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />
Maybe there is a problem with one of the animations for the shield? You could try a small shield. If this is the case, a un-install / re-install after backing up the saved games might help.
