On single player, locked on EASY difficulty. I killed the dragon the first time and the fight went like normal.

The second time, things went like normal (the dragon attacked me) until I had destroyed all the crystals. Once all the crystals were gone the dragon stopped attacking. It would not perch or shoot, it would just fly around, mostly inside the towers, acting like it does on peaceful difficulty or in creative mode. Once I killed it, the dragon flew to the fountain and blew up like normal.

I have NO footage of the fight.