History repeating itself
I looked up the cause for the infamous XP SP3 reboot loop at https://social.technet.microsoft.com/Forums/windows/en-US/40a0eecb-bc00-4746-8f5b-610891d7a73b/xp-sp3-and-continuos-reboots-on-amd-based-systems?forum=itproxpsp. It's an interesting read, a classical example of why Windows is flaky, also underlining their third party software dependence.
[Spoiler alert] Don't read the comments over there until you're through with my "explanation" ...
Windows XP SP2 & SP3 include a driver (intelppm.sys) which will blue-screen the machine early in the boot process when run on an AMD processor. Neither does Windows check the system type (Intel/AMD) before calling this driver, nor does the driver refuse to run on an AMD system. Instead, the initial OEM install had to have set a registry entry correctly (which some OEMs didn't), that had no purpose for XP RTM and SP1. When machines entered a reboot loop with SP2, which evaluated this registry entry, Microsoft provided a fix.
Have a guess: was it a) checking the system type before calling intelppm.sys? b) fix intelppm.sys to check for itself (which merely requires reading a single CPU register)? c) adjust the registry entry?
OK, you all voted for c), and that's what MS opted for as well. Some time later, SP3 ran into the very same problem. What had happened _there_? Some OEMs, in between SP2 and SP3, shipped their own hotfixes, fiddling with that registry entry again. Some SP3 beta testers had problems with that, so for the final SP3 MS decided to "preserve" the registry entry from being fiddled with during its own installation (apparently, the known-to-be-dodgy OEM hotfixes were re-applied during the process). Now, when people went directly from SP1 to SP3, skipping SP2, the wrong setting from the initial install was "preserved" as well and hence SP3 went into a boot loop again.
I have neither palms nor faces enough to express my feelings here.