Refer to your first pic-
IF the cable is too tight, the ratchet can't rotate far enough to release the pawl. It has to be able to rotate a "tiny" bit.
It appears you may also have a corrosion issue that could prevent parts from moving. IF something has to move from LIGHT spring pressure, it may be bound up.
I'm ignorant on "road" shifters and double ignorant on Campy as far as the actual mechanism/workings.
Maybe a flush with WD-40/real lube would help??