When the Ender Dragon flies to the center of the end island to hover above the portal and does the breath attack, she has issues turning around to target players behind her feet. In between breath attacks she will make an attempt to turn to players behind her but will stop immediately and not finish, proceeding to spew dragon breath at nothing.

This appears to not be intended because the dragon will properly target players positioned on the sides and front of her, but when a player is behind her she has trouble turning enough for her head to match the player's location and spews breath at nothing.

To reproduce:

1. Wait for the dragon to fly to the center where the portal is
2. Go directly behind her feet as she spews breath
3. Melee her
4. Notice how in between attack intervals, she will make an attempt to turn to you but stops too early, and will spew acid, letting you continue to hit her without moving
5. Repeat above on the other sides of the dragon and notice she will properly turn to you

The attached image is a diagram showing where the dragon can properly turn and the angle where she can't.