Currently when a player is sitting in an armour stand, and rotates, visually their head rotates at twice the rate of their body. The camera is still linked to the rotation of the body.

Here is a GIF that help demonstrate this,

https://gyazo.com/0e0f48d6249193aa8345255c8539121c

The current workaround I have been using is to rotate the armourstand to the rotation that the player is at, as the head is correct when the rotation of the armour stand is equal to the player.