A new Nether portal is generated after returning from a custom dimension while having a tamed mob

Brief description of the issue

Tamed mobs that normally follow their owner between dimensions, such as wolves, do not teleport with the player when the player enters a custom dimension.

Additionally, after the player returns from the custom dimension, a new Nether portal is unexpectedly generated at or near the tamed mob's location.

This can be reproduced with a completely vanilla tamed wolf and a minimal custom dimension.

Steps to reproduce

1. Tame a wolf.

2. Leave the wolf standing so that it can follow the player.

3. Teleport the player to a custom dimension.

4. Observe that the wolf does not teleport to the custom dimension with the player.

5. Return to the Overworld.

6. Check the area around the wolf.

Expected result

The tamed wolf should teleport to the custom dimension with the player, similar to how it can follow the player when traveling between vanilla dimensions such as the Overworld and the Nether.

Returning from the custom dimension should also work normally without generating any unexpected portals.

Actual result

The player is successfully teleported to the custom dimension, but the tamed wolf does not teleport with the player.

After the player returns to the Overworld, a new Nether portal is unexpectedly generated at or near the tamed wolf's location.

The issue does not appear to occur when the wolf is sitting.