After the Enderdragon is killed, the XP falls, but all of it falls into the end portal. I've tried to block it up so that there is a layer between the XP and portal, however, the blocks instantly break so the XP falls into the portal anyway. Afterward, a small amount of XP from the dragon is at the world spawn point, however, it's not many levels (around 4 bars for me). I and my friend have fought the dragon 3 times in this world, and all three times this happened.