Model Tilting Broken in Inversed Gravity

Issue with 2.2.12 Prerelease 1.

Tested using sloperollangle and the Halfpipe Utilities test map, using Jeck Jims' models (addon). (Oh, and Halfpipe Utilities itself, although it isn't shown much here.) Models go all over the place when tilted in the inversed gravity section of the map. Sprites are demonstrated to work as normal, both in Software and non-model OpenGL.