Despite the version, this has been in the game since I started playing in Alpha. Basically, when you go in a boat, minecart, or ride a pig, and go into F5 mode and back into First person, your arm model becomes crooked. Also, (in the second screenshot) this can inhibit the use of a map.
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Duplicate of MC-2963.
I don't think it is a bug, but I know that it's a bug when someone else is sitting on a boat, your hand also turns.