Something loaded must have been using Explorer to get the keys as they were pressed. The only way I know to mess with this is to get Anykey (for the scankey app inside), use scankey to get the keycode, and use that keycode in a hotkey in litestep, using lsslider or umslider to get bangs for adjusting volume.

Yes, that's a lot of work for two keys, if you're not used to this sort of thing.