Okay, so the material in question is just flashing and should not be in any way harmful to the operation of the firearm, according to Kel Tec.
However, they did replace the slide and the magazine I had sent in with the PMR. The magazines had been upgraded, but I was unable to get an answer as to why the slide had been replaced.
The front sight had been affixed off to the right, but I readjusted that. Other than that, I have had only a couple of issues: one with a misfeed that saw the head of a hollow point catch on the bottom of the feed ramp, and an outright failure to feed from the magazine. I'm unable to say if these came on the old/bad(?) magazine, since my oldest daughter wanted to go shooting with me, so I was distracted by Dad Pride to keep 100% track of things, so I'll have to go again with this in mind. The horror, right?
All ammo shot reliably, save for one round that misfired. The Gold Dots seemed to have the most potent discharge, which was odd to me, as I was also firing 50gr. Game Shoks. I was expecting somewhat of a bigger feel from the hunting loads as opposed to the lighter defensive round. Not sure why.
But yeah. I'm not sure why they simply didn't tell me about the flashing at the onset, but I guess I made the right call in sending it in as I got some new--and free!--parts.