When in survival and fighting the ender dragon firing arrows while the dragon is above her pedestal the arrows fire back (as normal) but they come back on fire even without a flame enchantment on the bow.
Linked issues
Comments 2
This is considered to be intentional, see MC-85910.
Wiki: "The dragon flies to its nest (approaching from the side opposite the player if possible) and lands on the highest block of the coordinates (x=0,z=0). The dragon is immune to arrows in this state (they all catch fire and bounce off)."