Teleporting away from a loaded entity (tested with 1000 blocks, don't know how it behaves with different values) and then returning by teleporting  (didn't test by returning without teleportation) causes the entity to duplicate, whereby one of the remaining entities has no ai and the other is still the normal entity. You can not interact with the newly created entity, nor does it do anything else. The only thing that happens is that it has a collision box so you still get bumped by it. The attached file is an example of the bug in action after having teleported away and returning for 3 times back to back. Relogging seems to fix the issue, but afterwards it can still happen again.