Yep. I wait until prompted by the installers, then reboot by clicking yes on the reboot y/n dialog. Never interrupt an installer unless you want to have a bad day.
Yeah, I've done a lot of searching and there's really very little like it. It's such a WEIRD problem. My best guess at this point is that it's something HP preinstalled that's breaking when it's no longer on HP gear. The big questions is what, why, and what to do... I'll keep kicking this football around for a bit.