Canon FD L 85 f1.2 lens help

I have a lens available to me but I found when I put it on my Canon AE 1P and put the setting to stopped down position it would only stay wide open when I turned the aperture control on the lens. The lens is the latest one that Canon put out but I know it is old lens but everything else on it looked very good. Is there I setting that doesn't work properly or is it defective ? He has used adapters on this lens and was thinking that might have changed something on the lens ? For the prices of these lenses I want to be 100% sure of proper function before I purchase it.

I contacted a professional Canon person benjiboy who suggested that the lens was faulty which confirmed my suspicion. The experienced people here are the best way to solve problems that may arrive with film cameras.