IN short, edit the in game keyboard commands or edit your f18keys.ini file so that the command CAM_ROTATE_UP is not bound to JOY1_HATUP. Something weird in XP seems to make it seem as if the Joystick HAT (whether you actually HAVE ONE OR NOT) is always in the UP position.Taking out this key binding will make your view return to normal.
Easiest thing is to edit the f18keys.ini file. Just remove the entire line or just edit out the right side so instead of:
JOY1_HATUP=CAM_ROTATE_UP
it reads:
JOY1_HATUP=
If you have defined and are using a custom key configuration, be sure to do the editing in that portion of f18keys.ini.