I have OptiFine_1.4.6_HD_U_C3 installed (the latest 1.4.6 version does not work, I don't know if that's just me or not) for the Ultimate pack and seemingly whatever settings I have it on world chunks periodically turn invisible for a fraction of a second. The result is a highly epileptic, unplayable world. Does anyone know what's causing this, or if Optifine just doesn't work for Ultimate?