As the title says: All extended/multimedia keys seem to get the NumPad (0x01000000) qualifier stuck to them after any key of the numpad has been used. This is (obviously) not the case for any other keys. To remove the numpad qualifier from the extended keys, any other key can be pressed (like 'A' or Shift...), this will "release" the stuck numpad qualifier. I gather this can only be a bug.
X1000, OS4.1.6+, USB keyboard.
> version
Kickstart 53.58, Workbench 53.11