I've got an M&P 45 full size, an M&P 45 compact, and an M&P 9 compact. I've shot thousands of rounds through them and I've never experienced the problem you've described.
Hope S&W takes care of this for you.
I expect Robo expressed the fix well. If it contines then send it back for repair. I've CC the M&P 45 for several years and haven't had the issue expressed unless I got lazy with my grip.
Those who hammer their guns into plows will plow for those who do not." ~ Thomas Jefferson