Wait, did you flip them skin side up or down at the start?

Damn right, same thing happened to me on a pressure vessel job a few years back. QC guy busted my balls about not squaring up my backing bar and I thought he was just being picky. Fixed it and my root passes stopped having those little cold laps I'd been chasing for months. Now I make my fitter check every damn gap with the gauge before I even strike an arc.

Man, that copper spike would freak me out too, but my old 12 valve has been through worse abuse than a Walmart parking lot. First synth change on mine showed a little extra metal and then it leveled right back out, so my guess is it's just the detergent doing its job and stirring up decades of crud. Your buddy in Tulsa might be thinking of the old seal shrinking issue, but that's more of a gasser problem from what I've seen. If the copper is still up at 6,000 miles, then I'd start sweating, but one sample is just one sample. Give it another change and see what happens, that's way cheaper than a rebuild.