The safety on an AR-15 is a trigger block. The trigger should not be able to pull when selector is in safe position. The hammer should have nothing to do with it. If the trigger moves while on safe:
1) the rear portion of the trigger that is intended to interfere with the selector is missing (ground away, broken off, etc)
2) the selector has a section ground out of it where it should not have been. Did someone try to make an M-16 selector out of it and not know how? A proper AR-15 selector is cylindrical and has only one flat spot, which is presented to the rear of the trigger only when in the fire position.
3) some very drastic way out of spec mis-location of the selector hole that allows trigger travel. i.e., the selector is located too far up on the receiver, by a quite significant amount that I doubt any QC person would have allowed. Does the detent snap? Or does the selector move freely? That would be a clue.
I can't think of anything else. This problem should be very conspicuous simply by popping out the rear take-down pin and having a look inside.
It is possible that a similar condition existed with the trigger, and you incidentally rectified it while dealing with the hammer. I'd double check the trigger pin to ensure that it is not borderline.
There are various brands and types of anti-walk pins available in the aftermarket. You wouldn't be the first to discover that bump-firing sometimes requires them.
I recommend these: http://www.midwayusa.com/viewProduct...tNumber=539753
The ones that have the tiny screws can come unthreaded or break the itty bitty screws, not recommended.
No doubt, contact with the manufacturer will result in the same suggestion.
You cannot, and should not attempt to, stake a steel pin against aluminum. The thin layer of anodization will flake off, and the pin may appear retained for a while, but you will have cracked the anodization from the surface, even inside the hole. It will result in elongation and over-sizing of the axis hole. It'll seem fixed at first, but time will show you that the receiver has been ruined, possibly beyond (reasonably priced) repair. I'll say it again; DON'T DO IT.
Just buy the anti-walk axis pins. They're cheap.