Skeleton's Armor doesn't rotate to the 90' angle of its arms in my resource pack and/or default

Skeleton and zombies' arms are both rotated 90' relative to the player's. On the rare occasion a zombie spawns with a chestplate, the arms rotate to the same 90' angle as their arms. However, if a skeleton spawns with armor, the arms on the armor don't rotate with their arms. The attachment shows my texture of golden armor from my WIP resource pack on a skeleton; he was randomly generated in a cave. The gun is his bow, and those are his arms protruding through the armor.

What I expected to happen:
The armor would line up with and cover the skeleton's arms.

What really happened:
The Skeleton's armor rests at his sides as if he were dead. (pun not intended)

How to reproduce this issue:
1. Find a skeleton wearing armor, or spawn one in with an external program such as MCEdit.
2. Notice that the arms' armor does not rotate 90'.