Hi folks...had a problem I fixed myself and just wanted to share with you all.
I've been carrying my M&P40 in a Comp-Tac C-T.A.C. IWB kydex holster. I'm not a big guy by any means, but I had found that while carrying my M&P, the mag would get released while it is holstered on my hip! I suspect it's due to the mag release's ease of activation coupled with it's extension from the pistol body. I tried moving the button to the other side of the gun, but I'm just not comfortable with activating the release with my index or middle fingers.
To solve the problem, I removed the mag release button from the gun, secured it in a vise, and dremeled about 1mm off. Reinstalled in the pistol and there's still plenty of material for me to intentially activate the mag release, while removing its ability to be inadvertently pushed while holstered.