If you look at yourself (F5) in a minecart, or if you look at the character within the inventory, you can see the hands are tucked into the minecart. The graphical bug is probably due because of this 'tucking in' feature.
The problem was that this never happened before in 1.5.2. And now that this is happening only in a server, and in the snapshot. It me worried that it is a bug, or that sprint has been made server side.
If you look at yourself (F5) in a minecart, or if you look at the character within the inventory, you can see the hands are tucked into the minecart. The graphical bug is probably due because of this 'tucking in' feature.