I get a kernel panic on system shutdown on Mac OS X 10.5 9a527, and the problem appears to be in the kext unloading process. I can also cause a kernel panic by manually unloading the KEXT using "sudo kextunload -b com.baltaks.driver.DoubleCommand".
Attached is the kernel panic dump I am presented with on restart. I have reported this to Apple using the kernel panic crash reporter UI.
kernel panic dump