It happens with a lot of different brands of pistols. My opinion is it's fine if you are playing games, but I wouldn't like it in a self defense situation and the reason being is this. Whether this will happen with M&P's I don't know, but I had an officer tell me his dept issue Sig P229 40s&w was malfunctioning. He said it wasn't chambering a round when inserting a partially loaded magazine during a drill. We were able to replicate the issue easily and what was happening was he was inserting a 1/2 loaded magazine with enough force to cause the rounds to compress the magazine spring and in turn when the slide went forward automatically it wasn't able to strip off the top round. He had to recycle the slide to chamber a round. Like I said, I don't know if this will occur with the M&P mags, but it's something to keep in the back of your mind...if it should just go "CLICK"