Sitting in minecart is higher than it should be

When riding in a minecart on 1.5.1 the player is seated higher than he should be.

This can sometimes be worked around by getting into a minecart on a hill, but getting into a minecart on a flat surface almost always produces this result.

I'm attaching a picture of the correct behavior, and the incorrect behavior when getting into the same minecart on the same rail.