I have had this problem before already once, this is probably a dupe, I searched, but I could not find it (I am really bad with tags). So I tought lets report it, because I can't find it, so it might not be reported.
You can see it in this video:
http://youtu.be/Cvn640U2RhE

PS: Just a reminder. I am testing some things with EnderDragons atm. Arround 50 blocks behind me there is a NoAI Enderdragon.