I have the M&P 9c and I haven't had any problems. I'm 6'3" with pretty large hands and I shoot the 9c at least twice a week.

On the other hand (no pun intended) it does seem to be an issue discussed on the M&P site and the solution for many appears to be to change the mag release button to the other side. I don't think you could get a stronger spring.

I just looked at the way I grip the pistol and my left hand doesn't really come that close to the release, so you could look at adjusting your grip.

Hope it works out

Dave