Fast Startup, genuinely
Fast Startup (hybrid boot) writes the kernel and session-zero state to hiberfil.sys at shutdown. On power-on, that image resumes; user sessions are logged off, so per-user settings re-load — but anything kernel-side (driver state including some keyboard controllers) comes back cross-fade from the hibernated snapshot.
Why this corrupts testing
Edit key → Shut down → Power on
kernel state resumes from image — your edit didn't get a chance to drive the boot path
Edit key → Restart
full boot path: kernel re-init, drivers re-load, settings re-read
That's the whole “it worked until I shut down” genre: Restart bypasses Fast Startup; Shut down doesn't.
Proof discipline
- Test with Restart, not power cycles, when validating any boot-adjacent tweak.
- On desktops where hibernation is admin-controlled, note you're editing the one boot-path the user can't reach with a per-user tool — document the behavior instead of fighting it.
- Audit
HKCUvalues after a real restart before concluding anything won’t stick; most “reverts” are replayed hibernation state, not rollback.
ProofTune ProjectEngineering notes — every claim here names the bytes a real tool touches. Verify first, install second.