Just hopped in a Mortar Bike and this happened (note mortar on the right, sky and textures of cockpit):
http://img245.imageshack.us/img245/6244/oddgs8.png
Happens too in single player on the third/fourth mission for some reason, disabling bmp mapping fixes the issue, just something i thought i should bring up,
Cheers.
bmp mapping? Do you mean bump mapping? (two different things). Just means your card is not capable of it (BZ2 uses a *very* old technique before there was a 'standard' way of doing it, so it works with some cards and not on others). So don't use it. :)
Might also be that thing's bumpmap texture is messed up somehow...
lol, sorry my bad technical lingo, its not so much of a problem i dont really pilot the mortar bike, but thought may be of interest, thanks anyway