Stop immediately! I am not sure if you are talking about the same thing but anyway ...
Friend's ProSport had this problem, eventually he 'cocked it' except it wasn't cocked, it was just held on the anti-bear-trap, when he returned the cocking lever to its normal position the rifle fired, smashing the piston into the cocking lever and smashing the fore-end under the tip of the cocking lever.
To cure
1. Order a new bolt from Chambers, as the old one might have become stretched.
2. Strip the rifle.
3. Thoroughly check the hole in the sliding piston to make sure the threads are OK, and degrease.
4. Degrease the new bolt.
5. On reassembly use thread-lock on the bolt, and make sure it is tightened properly.