I have a script that creates a bunch of rotated and scaled bitmaps (they're walls in a video game level). About half of them were turned completely black, and I noticed that this was the exact same number that had negative rotations. Since they are basically lines from one point to another, I had the script take all the ones with negative rotations, put them at the second point, and rotate them +180 degrees so they'd have positive rotation, but I still had the same problem. I also tried doing the same but making _xscale negative, and the problem still wouldn't go away. Finally, I replaced the bitmaps with vector rectangles, and noticed that the ones that had previously been blackened now had emboldened lines.

I don't understand what's causing the problem. Has anyone else ever seen this before?