I've read that article a few times, and still trying to debug the problem. But I'm out of town right now so can't do anything until I get home. A few things I think may be the problem:
It only started doing this recently, so the spring may be getting old or feedlips may have spread a little. It consistently happens when there are two rounds remaining in the mag, and with two rounds in the mag the follower is too far below to be making contact with the slide stop. I think somehow the top bullet is making contact with the slide stop -but how? It could be that the spring is weak and allowing bullet bounce in the mag during recoil and that is what is activating the slide stop, or there is too much slop in the feedlip dimensions -once again allowing the bullet to move around during recoil and contacting the slide stop.
This happened with this mag when I first got the gun, and a new spring/follower kit from Grams fixed it. So have a few new springs on order, and we'll see what happens when they arrive. I do recall beveling the sharp edge of the follower at tad to get it to clear the mag catch hole... I'll also mic the mag lips when I get home to see if they are out of spec.
I thought long and hard about disabling the slide stop all together, but so far I haven't done it -and I don't think I will if I can get this mag fixed. I hardly ever go to slide lock in Limited, but I do in L-10 and IDPA so want to keep that feature for consistency.
My other two mags (bought them new) are still going strong. It's just the one mag. That'll be my third mag/barney for now until I get this debugged.