I have a quite simple DirectX program. It uses the data of .x files to load a mesh. It worked fine on XP.

I bought Vista and tried running this program on it. I succeeded, but I found a weird problem.
The program rendered a cube, but Vista somehow uses the same file to render a rectangular prism.

I have controlled twice, that I haven't changed the program's code or the .x file. On Vista the program is also much slower, although the computer, that Vista runs on, is more powerful than the computer XP runs on.