I'd still stand by #1 being a spring issue, and #2 my guess would be Gander opened it up and stuck it in the case, and someone put it next to an older Glock and played around with them and things fit, so they got mixed up getting put back in the case. Still "new", but I'd bet "display"Great that the OP got taken care of, but I'm still wondering:
1) what was wrong with the NFML mag that wouldn't allow it to function properly in a Gen3 pistol
and
2) why GM would be selling a 3-year old pistol with even older mags as "new"?