Moving perpendicularly into a diagonal wall causes sliding.

[Gayo]

Expected behaviour: If you hit a wall by moving directly toward it (along the normal vector), you should stop in place rather than sliding.
Observed behaviour: When you bump into a diagonal wall while moving perpendicularly to it, you will usually, but not always slide along it.

[Gayo]

This is likely an issue with subpixel movement, with characters moving up and then sideways in alternation since they're not positioned perfectly in the middle of the pixel.