in 16-bit, wbuffering is enabled.. disabling it might sort out the problems.. problem is, older cards will dislike this even more. I think in 32 bit, w buffer is disabled naturally. With the above also, are you using blitz 1.89? it might also be that "fixed bug" that got "moved somewhere else" with the vertex corruption stuff.
Theres alot to try.
Theres alot to try.