Mobs and particles sometimes don't fully render behind stained or tinted glass
Entities partially or fully disappear behind colored and only colored glass in specific orientations or when f1 is pressed.
Reproduce
1. Use any graphics mode other than fabulous
2. Turn off entity shadows
3. Place a two high pillar of stained glass
4. Use spawn egg to spawn a cow behind pillar
5. Move side to side, every now and then the cow will disappear