Only tested in the nether. If you place a minecart and right click it to get in, you crash. This was on a server so the other player sees you get in the cart and the cart and you disappear. Every time you try to connect, you crash. The other player on the server sees you appear for a second in the cart, to fix the issue the other player can break the cart in the second the player is there, after the cart is broken, the player can rejoin and everything is fine.