Mr. B: Based on your initial description of the situation it has to be a problem inside the bolt or perhaps something external to the bolt interfering with the free movement of the cocking piece. Personally I'd strip that bolt down and give it a very careful going over before using it again. You have other functioning bolts to compare the parts with which helps. After going over it you can submit detailed comments/ photos and Capt. Laidlerand others will be able to help you solve the problem. What you learn will also help other non-experts like myself.
Ridolpho