If you get some debris in the channel that the bolt slides in, you can end up with a sticky or even stuck bolt. I have a K-38 that came to me with a problem bolt, and I had to keep running dental picks and strong toothpicks through the groove until I got rid of whatever the bolt surface was grinding against.
A less likely and perhaps more challenging problem involves something that is keeping the cylinder center pin stuck inside the ejector rod. If the center pin is jammed, you can push on the thumb release until the cows come home and you won't get it to move.
A final possibility is that the bolt got moved so far back that the round end was dislodged from its travel path and now barely overlaps the edge of the hole in the frame through which it contacts the center pin. Tapping the gun with a nylon handle screwdriver or some other non-marring mass might dislodge the bolt in this case. In fact, if this is the problem you may be able to just put a thin wire or a fingernail under the thumb release and pull/pry away from the frame. You only need to move a few thousandths of an inch to clear this kind of jam.
If that doesn't work I don't think there is any harm in taking off the thumbpiece and seeing if there is anything that might be causing the jam. It's OK to manipulate the threaded post of the bolt that protrudes through the frame, but be careful not to damage the threads or you may have trouble getting the screw cap back on the post. The primary value of trying this kind of approach with the thumb release off the gun is that you are less likely to mar the finish because you can use needlenose pliers to grip the front and back edges of the little process on the bolt that rides in the slot in the frame.
Good luck. Let us know what happens.
