This is more of an improvement request than a bug, but there was no way to change it in the "issue type" field. This issue also applies to all versions of Minecraft that 3D Anaglyph feature is available.

The seperation between the Cyan and Red images in Anaglyph mode is too large to be usable during gameplay. One has to be at great distance from the screen (more than 2 meters for a 22" screen) or use a tiny window for the game, in order for the eyes to focus at all, and even then the strain is too big. Ideally a slider would be great but that is a whole new feature request so I think we all can settle for a tweak now.