1.7.x not playable after playing 1.8.3

After installing and playing Minecraft 1.8.3 via the launcher, 1.7.x becomes unplayable.

It is my guess that 1.8.3 updated a dependency that 1.8.x was prepared to handle, but that 1.7.x was not. If this is the problem, the launcher should probably separate dependencies between the two. Though this is only a guess, as I do not know much about the two.

Crash Report attached.