I know you said it was designed to not get trash in it, but if the rear of the disconnector (better describes as the spac e under the disconnector) is open at all, trash can get under it, preventing it from getting full movement and thus holding onto the hammer. The description of it not budging fits this to a "T". When you open the gun, it normally gets moved enough to move the trash out of the way, thus the suminabitch works ok. Trash can be the cup of a primer.......... don't ask how I know
If it is all sealed up, something inside may have given up on you.