Hi Tom12345
I think (I am absolutly NOT sure) that the problem is the front-back node.
Infact I think that OGL doesn't support front-back material (I tried in 3dmax too).
So XSI create a sort of interpolation between front and side color (and texture).
If you apply a white texture in front and for example a blue color in back you will see a light blue texture on your object. (2 textures are not interpolated).
Finally I think that this is not a bug, but a OGL limitation.
But I repeat, this is just an idea, I really am not expert about OGL.
Hope this helps
Ste