Worldborder + boat bug

Steps to Reproduce:
1. Throw ender pearl through the worldborder
2. Place a boat out of the worldborder
3. Swim to end of the world

How does this bug looks like in Minecraft 1.8.8: https://youtu.be/yXChgr0oOAM
How does this bug looks like in Minecraft 15w47c: https://youtu.be/PaLvgWPjvZk