My M&P 45c does that too... I have to hold the lever in the open position or it will spring back on it's own, even before releasing the slide. It didn't do that when new (I think.... maybe it did and I just don't remember! I may be confusing it with my Sig which of course stays open)
I'm picking up a full size M&P this week, I'll see if it does it too.
Last edited by cowboy1964; 01-22-2012 at 22:30..