When you give yourself a skull for example /give @p 1 3 {SkullOwner:notchhead} while in offline mode, it will crash your game. It should just give you a normal Steve head.
Linked issues
Comments

When you give yourself a skull for example /give @p 1 3 {SkullOwner:notchhead} while in offline mode, it will crash your game. It should just give you a normal Steve head.
Ryan Yilmaz
(Unassigned)
Unconfirmed
Minecraft 14w34c
Retrieved
Please include the crash report.