Items can be dropped in the worldborder when outside and will float / get stuck

1. Create a worldborder
2. Teleport outside
3. Look almost down
4. Throw an item

The item gets stuck in the worldborder

Since 14w29b it seems like this bug isn't happening so extreme any more, now you have to move away while throwing the item and also the item gets after about 1 second to the "right" (right is quoted because it is still floating 1 block above the ground) position at the ground