And on a possibly-related semi-tangent, testing "strange" keyboards often produces bizarre results.
My standard setup is an F-122 running though a Teensy connected to a non-powered (good-quality name-brand) USB hub. In general, this works properly and boots consistently.
When I test a USB keyboard or mouse, I hot-plug it in to a vacant USB port. Often it works immediately, but sometimes a re-boot is required.
PS/2 keyboards are far more problematic. I assume that it is a given that they have to be recognized in a re-boot. But often, even with my standard "go-to" keyboards (a Model M, and a Northgate Omnikey and a Dell AT101W, both modded and transplanted with better switches), as well as many of the strange and obsolete new/old keyboards that I have bought, I often get boot problems, crashes, BSOD/"restore to earlier configuration" and other time-consuming and meaningless nonsense. Sometimes multiple iterations are required to get back to ordinary life.
But here is the weird part: with the computer completely "shut down" but not actually "off" via the hard-wire switch in the back, *sometimes* the PS/2 keyboard will cause it to boot by plugging-in, un-plugging, or sometimes even just pressing random keys!
WTF is that all about? Non-techie that I am, it almost seems like BIOS-level stuff!