To recreate it - simply spawn a mob set your spawn point near that mob and die few times from him after death mob has chance to become "Ghost" And you cant hit him to fix it you need to re enter the game
Video:
http://youtu.be/i6fUAP8qR6Q
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Duplicate of MC-2713, please use the search function to see if your bug has already been submitted. Currently over 47% of tickets are being resolved as duplicate.