Ender dragons can pass through the world border

The Bug:

Ender dragons can pass through the world border.

Steps to Reproduce:

1. Set the world border's center to your current position and to fifty blocks wide by using the commands provided below.

   /worldborder center ~ ~

   /worldborder set 50

2. Summon the ender dragon by using the command provided below.

   /summon minecraft:ender_dragon ~ ~ ~

3. Wait around thirty seconds and watch the ender dragon closely.
4. Take note as to whether or not ender dragons can pass through the world border.

Observed Behavior:

Ender dragons can pass through the world border.

Expected Behavior:

Ender dragons would not be able to pass through the world border.