I recently found another odd thing: one of my mags is not dropping free when I try to reload. What I found is this: when I press the mag catch, I hold the gun a bit tighter; apparently tight enough to squeeze the grip (STI plastic) a tiny bit which is enough not to let the mag drop free. If I hold the gun in left hand on the frame, not the grip, and press the mag release: voila, it will drop free ...
First I thought it is the mag catch, because when I looked down the grip inside, I could see a tiny bit of the mag release poking into the grip. I filed this down until I was positive that it was not the mag catch. With all the try and error, I found that the flexing grip is the culprit.