When reloading a single player world, or joining a multiplayer world, any moving minecarts are rendered in the wrong place. They are shown moving around several blocks away from where they "really" are. This glitch sometimes fixes itself a random amount of time later if you move around but I could not reliably get this to happen.
Duplicate of MC-2783, please use the search function to see if your bug has already been submitted. Currently over 55% of tickets are being closed as duplicate.