The bug:
The player's head when returning from spectator mode looks in the completely wrong direction
To reproduce:

Get your main and alt (or friend) account, open up a server and join with both accounts. 

On one account, press F3 + N to go to spectator mode

Move a little bit

Press F3 + N again

What is expected to happen:

The head is facing in the direction the body does.

What is happening:

The head is facing at around 180° off the body / looks backwards.

No, this is not a duplicate, it's another issue but it's (hopefully) not invalid like how my previous was. I was able to reproduce that bug, but the previous one has been marked as solved and I thought I shouldn't modify that.