A few weeks ago, a member of my server contacted me about an auto-teleport bug that only occurred when the player went under y=2 (or y=3, it changes depending on your area.)

The End seems perfectly normal, other than the End Portal to The Overworld and the portal to the Outer End Islands are made of obsidian, and the fact that there are significantly but still functional smaller portals in the End Void.

This was re-created in vanilla, by the way (we did have a certain texture pack but I took it off a while ago.) 

I am certain there are no active command blocks in this Realm.

It happens at all coordinates across the entire map.

If the player slowly went to y=2/3, the issue still occurs.

Steps to Reproduce:
1. Dig down or find a spot that is close to y=2.
2. Go to y=2
Observed Results:
The player (you) gets teleported to The End Dimension.
Expected Results:
Nothing should happen.