I expected the dragon to fly around normally in the overworld.

It stayed in the middle aka the "invisible" base. Then it went foward and did the same thing.

1. do /summon EnderDragon in the overworld
2. wait until he flys around a little
3. he will spends 5 seconds in the same place then go fly around and then go forward and repeat step 3 and he occasionally fires the paticles