Interesting to say the least. But since you seem to be one of a very few with the problem, I would say the M&P's are not plaqued by this. I have heard this before, but not in a while and it only affected some of the earlier models. I have at least 5 different holsters and 4 different M&P guns and have never even remotely had a problem. As for trying the mag with the slide off the gun, makes no sense, as I don't carry the gun with the slide off, seeing the amount of spring travel does not matter to me, it works.... I've checked all of my guns for a light spring, everything seems normal, I've tried empty and full mags, normal. When I install the mags I hear and feel a very sharp and distinct click. No matter how I push the button or hold the gun, unless I have my finger on the button and push it, it ain't falling out.. I don't see anywhere on the holsters to make contact with the release button, so the holsters aren't the problem... from what I see, the only reason your mag falls out, if everything is as you say ... is your finger or some part of your hand is pushing that button.. maybe you just have one of those hands that needs to go back to the factory for adjusting.. jkg.. it's stuff like this that makes me wish I could see it first hand. Because I just don't see it from the info you gave us, something seems to be missing. Have you tried other magazines, newer ones? If it is that bad, I would absolutely send it back and insist it be made to work properly.
