The problem is the new player identifier. A player used to be uniquely identified by his Name, which is why renaming your character was just impossible, since the game would register a new player instead.
Starting from Version 1.7.6, specifically Snapshot 14w10b,
[...] All server files that are intended to refer to players will be automatically changed to go by UUIDs (=Universally Unique Identifiers), and you do not need to do anything. [...]
emphasis and parenthesized part mine. This means, that the correct command to spawn Notch's head is no longer:
give @p skull 1 3 {SkullOwner:Notch}
but, according to the description of this video:
give @p minecraft:skull 1 3 {SkullOwner:{Name:"Notch",Id:"069a79f4-44e9-4726-a5be-fca90e38aaf5",Properties:{textures:[0:{Value:"eyJ0aW1lc3RhbXAiOjEzOTczMDc4NzUyNjMsInByb2ZpbGVJZCI6IjA2OWE3OWY0NDRlOTQ3MjZhNWJlZmNhOTBlMzhhYWY1IiwicHJvZmlsZU5hbWUiOiJOb3RjaCIsImlzUHVibGljIjp0cnVlLCJ0ZXh0dXJlcyI6eyJDQVBFIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvM2Y2ODhlMGU2OTliM2Q5ZmU0NDhiNWJiNTBhM2EyODhmOWM1ODk3NjJiM2RhZTgzMDg4NDIxMjJkY2I4MSJ9LCJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvYTExNmU2OWE4NDVlMjI3ZjdjYTFmZGRlOGMzNTdjOGM4MjFlYmQ0YmE2MTkzODJlYTRhMWY4N2Q0YWU5NCJ9fX0=",Signature:"aT80QC+msQMaew55CcyxRF8VpCsuHLJvEQNbsdQTSi4v2VACgGXEkLZkmMIWwOdUgeT+juEbzNCNPf3knDn56W4HKqS/f0ppMUHoWPXl4/XWHsfxG7iSwq6MkBF90GwqGEjCBuDG4ZQnHpEOBQXxa8bmrhZoXJjMBXhO3EAiB37Hb7V+C1xX9H5p+JkzXao1Ca3WEYimC+2QQa3gGoPIrHR/4c47EbZj7cuGarQzTdCyZEYd3adFF67oFOhgmiYYHIabT2d5Ejh5PTwJHIjKGw1Uo+qjrEeBWKTFHZ86t5eSa8pZGkmjxFxn2oaKUz8PsopW5b5DlS3CiZo3IQE0oa8Fisncoab1pIsj0P80rrugTBRCg/pbEJls7dUpJs5l3xJ7XFujYT8a7O0bjksX87z9KJHOfsN5LjFoQS6oA5qDXu2Fy6loYZy5h2XnjcWQzWHZWwaxgJPKYIS8zjx63ussFy3JhaCNp5BVqQKRbB6wzGt2nXScBKhPUf76eJViIpBVfZ1ZerYCMyj0GKdhu3DnLMrK1qbi05IzKGNzGoDZfTxh6wZtXJFMTXk1EO/sAAiMgN3OpFn3IV8YA36rDkindA4LZI327dQVmvV9Rt3/U8J7n4bNLJRRfgXsZbg+Yn7yF20+Z3Qkfm80kTiu2hci1Dl2A7dscahBjD08JLE="}]}}}"
When you place the head down, it will be automatically converted into the new format, but not when you wear it. It's a known bug, that is fixed in upcoming versions, probably 1.8 release or a newer snapshot.
For now, try placing the head, break it, pick it up and then wear it.
Best Answer
Yeah, it's a bug, which you can read about here:
http://bugs.mojang.com/browse/MC-86138