A friend asked me this morning if I'd ever heard of this, which I haven't, so I'm asking you experts.
He swapped the bars and shifters from one frame to another, but when he went to hook it all up, he says that the right shifter won't ratchet. It has one of those clear 'gear indicators' and he says when he pushes the lever over, the indicator shows that it's pulling the cable, but it doesn't click, or ratchet, at all. As he releases the lever the indicator just goes back to the far left.
I personally don't own any 7800's so I couldn't tell him what to look for inside, but I'd appreciate any advice you guys can give.