When optifine is installed, the white stained glass, which is supposed to look like normal glass, and the light gray stained glass, which is supposed to be invisible, have their CTM appearance, overwriting the desired look.

This can be fixed by adding the CTM textures to the pack and overwriting them.

A moment of silence for my fully vanilla stream ending. It started in 1.3, and ended now as I needed to test the fix.

White stained glass will have the connected textures of normal glass.