Ender Dragon flies down in the void when the exit portal is destroyed

The bug

If the exit portal is removed and the ender dragon tries to perch, it will fly to y=0. Doesn't matter if it's a hole or not, it will go through blocks tho.

How to reproduce

1. Enter the end.

   /execute in minecraft:the_end run tp @s 0 100 0
   

2. Remove the exit portal (make sure the enderdragon is alive).

   Stand on top of the exit portal and run: 
   /fill ~-10 ~ ~10 ~10 ~-60 ~-10 air
   

   → The ender dragon flies to y=0, if it wants to perch.

Code analysis

Code analysis by [Mod] Chandler can be found in this comment.