ootisg

I can confirm for 20w19a

To my knowledge, this would happen because of a discrepancy in how the game checks for portals. It does not check for portals within 1024 blocks; instead, the radius it checks is 128 blocks. However, in the nether, coordinates are multiplied by 8. This means that building a portal in the overworld within 1024 blocks of another will not create a new portal in the nether. However, creating a portal in the nether more than 16 blocks away from another portal will result in a new overworld portal being generated. The portals are generated at corresponding locations, and the now match up, meaning the portals link to each other fine.

However, say you had one portal in the nether, and then built another portal in the overworld less than 1024 blocks away, but more than 128 blocks away. The closest portal within 128 blocks (when going from the overworld to the nether) is now the original portal. Both overworld portals link to the same portal in the nether. If you destroy the first portal you built in the overworld, the second portal in the overworld and the only portal in the nether are now linked. Going to the overworld to the nether won't cause a problem, as when your coordinates are divided by 8, the new location is within 128 blocks of the portal in the nether, and you are placed at that portal. Going back, however, will cause a different behavior: you will create a new portal. This is because when your nether coordinates are multiplied back by 8, there is no longer a portal within 128 blocks of that location in the overworld.

This is a very long and complicated way of saying that this most likely works as intended.

This bug is back in 1.9, but only affects fireballs, small fireballs, and dragon fireballs.

How do you delete a bug report?

/replaceitem entity @a slot.armor.head wool 1