I pulled out my 4506, basically the same gun with regards to the fire control mechanism. The only way I got a dead trigger was not fully inserting the magazine or the slide not being fully in battery. The mag safety works by the back of the magazine body lifting up the ejector. So unless the ejector is broken off (I have had that happen ) as long as the mag is fully inserted I doubt it has much to do with the magazine safety. Something keeping the slide from running fully into battery would be my guess.

Of course that rube Goldberg frame mounted decocker may be coming into play, but I don't know how a change in ammo would cause that to malfunction.