Powerbook G4 panics on every restart

I have a Powerbook G4 that panics on every warm restart. The restart can be triggered by Apple/Restart or a software update or even a sudo reboot. All cause the panic as it comes back up.

The weird part is I can do Apple/Shut Down and wait for a power-off, then power back on, and it starts up normally.

To sum up: restarts cause a crash every time, shut down / power up starts normally.

Any ideas? It's running Tiger 10.4.11