I took my bike (Campagnolo friction gears, 2x7) from winter storage and ran into some misbehavior right on the first ride: whenever I shift to any of the three largest rear sprockets, the derailer shifts slowly back after I let go of the shift lever, eventually coming to rest on the fourth sprocket.
I hadn't adjusted anything when the bike wasn't being ridden. I have no experience of maintaining a friction shifter system, but it looks to me like the shifter cable had been under too much tension through the winter (ie. wrong gear) and bent into a position at the shifter, and now wants to return to that position if I shift past it. Does that happen? Is it plausible? What else could explain this?
(FWIW, I'm no luddite and have no particular reason to ride around with a friction setup as opposed to an indexed one -- I bought this bike with the sole intention of converting it to a fixed gear, but I've been enjoying it too much with gears to go ahead with the plan just yet. )
It *could* be the cable has stretched. I see bent cables near the derailler and a good tightening will usually fix it. Also, since its friction levers, the tightening screw could be loose. If its campy (don't know what year yours is), there should be a loopy kind of metal. Designed so you can tighten it as your are riding.