Harry Potter Effect
The "Harry Potter effect" is a texturing glitch that appears only in newer custom tracks. That's because newer track models are created with the BRRES Editor, that currently has this glitch. This bug won't happen if you use only the SZS Modifier to create your custom tracks. It's named like that because of Harry Potter's invisibility cape - it's not invisible, but it covers what's behind it.
This glitch happens if the transparent polygons in the BRRES file appear before the normal ones. The previous polygon will always appear on top of the later one, even if it's transparent.
To fix it, you need to have the transparent polygons as the last ones of the BRRES file. To do this you have to set the transparent polygons to be the last ones in the OBJ file. In 3DS Max you can set the order of the polygons. Google Sketchup uses the texture names for the order, so you need to change the texture names so that they're the last ones.
This will, however, still happen if a transparent polygon is behind another. To fix this, you have to change the order of the polygons even more.
Example Video
Tutorial how to fix it
1) Open your BRRES file with BrawlBox 0.65c
2) Go to 3DModels> course> Materials
3) Go to every transparent material shown here, and make EnableAlphaTest true
4) Click the + on each texture in the materials folder of the MDL0, including the nontransparent ones, and make the scale (1,1) for everything instead of (0,0) (or else the track will be all solid colors).
5) Save it.
6) You're done! Now just reimport the BRRES file to the SZS like normal.
7) Test, and if anything went wrong make sure you didn't unintentionally change anything you shouldn't have.
Thanks Voldemort, AKA Baoulettes!
Anti Harry Potter effect
This is an even more crazy glitch we discovered.
UPDATE: Just an error on BigOto's part. Accidentally set DepthFunction to "Greater" instead of "Less or Equal" like normal.