Point taken, Rob. I shan't fault the gun if it turns out to be the mags. It did begin malfunctioning the first year I got it, after only a few hundred rounds. I should have had it taken care of under warranty then, but my life was really busy, and it still functioned okay, just didn't lock back the slide (okay, I was lazy, and not really into guns then...).
The grips are just snug, with a dab of lightweight Loctite to keep them from working loose.
It really is just locking back with one round left, not failing to feed. It only happens about one mag out of ten. Unfortunately, I haven't kept track of which mag is which to see if it only happens with one mag. I'll mark my mags next time out. Oddly, it never happened until the smith fixed the pistol with some minor work to the slide and slide catch.
Thanks again for your help - I'll post when I get the new springs and followers.