If I understand it properly, I *think* that Optifine bypasses several parts of the normal Forge rendering engine in order to get its higher performance. They do this knowingly, and do so actually
expecting it to screw with the visuals / performance of a number of mods. I suspect that they do not know of any other way around the problem so they just write off mod compatibility completely nowadays. The real sad part is that I have discovered
FPS Plus+, a mod that easily doubles or triples my framerate, and it does not screw with rendering at all. I get smoother gameplay (due to the higher framerates) while using it and it doesn't actually hose up any visuals.