I just called tha number... 'n they're sending a packet of screws/ I'll use that Lok-Tite. 'Still doesn't explain how my mag release was depressed.
Your mag release is not protected by the Serpa (I don't think), it's actually exposed to the inside of your body and if you aren't 100% sure that the mag is seated it most certainly can be an issue.
Something I've noted with my Glock 34 is that the extended mag releases can be where a problem will lie in that they extend toward the body enough that with the right type and amount of twising you can hit the button with your body and not realize it...not much, but just enough to be a problem.
The other issue is that the edge of the kydex can be really close to the mag release button, depending on the firearm. Extended mag releases are a bad thing in this situation as well as a firearm that doesn't seem to seat in the Serpa properly or shifts slightly in it.
Unload completely and verify that status. With your Serpa off your belt and in your hands, seat the 1911 and lock it in place. Then observe where everything is in relation to your particular issue. Now you can twist, move, and shift the firearm in small amounts (don't us a lot of force, that may break your holster) to see if you can replicate the problem.
I had a friend complain about this with his XD and I discovered he had an extended ambi-release for his mags and his seatbelt hit the release button. Something to think about.