visible chunks load and unload for no reason. tested in 1.8 and 1.8.1 (discovered without optifine. used by mistake in screenshots) also tested on 5 different computers. please see this video to see the issue in more depth (screen shots don't cut it)
Environment
linux (ubuntu) / imac (10.6.8) / macbok pro (10.8) / windows xp & 7 / 1 core / 2 core / 4 core
Dupe of MC-63020