[Mecanim] Turning animation doesn't rotate the whole way

So I'm trying to figure how best to do a character controller for a point and click adventure game. I'm experimenting with using root bone movement to handle character movement, but mecanim is giving me all kinds of sass.

I have three animations. An idle, a walk cycle, and a 180 turn. However, the 180 turn results in some weird issues.

After a couple of loops though, the final rotation slowly get's out of alignment. In action, it looks like this (look at the blue arrow)

Ideally, he should be turning 180 degrees evenly, so in my animator when it switches between walking and turning, he should be walking in a perfectly straight line. Instead, overtime he changes direction. The animation is correct in 3ds Max, so I have no idea of what could be causing this issue.

I have already tried turning off animation compression and redoing the animations using idle frames to ensure there's no weird blending issues.