Hi, I was play testing in the new 1.18 in my single player game and found that the nether portal I built under ground (at y=-52) created a portal to the nether dimension(I somehow portal onto a nether fortress above lava lake). However, the portal generated in the nether does not connect to the original portal I built in the overworld, but generated a new portal above ground. I tried to find the source of this bug. and I think it might have something to do with the original portal being at y<0, which caused the portal in the nether to generate a new portal in the overworld instead. To prove my point, the portal generated from the nether to overworld is about 8 times greater in coordinates, which is exactly the coordinate conversion from nether to overworld.

As for the coordinates:

Original portal built at: x51 y-52 z323

Nether portal generated in the Nether: x22 y68 z44 (at the nether fortress above lava lake)

New overworld portal generated by the portal generated in the nether: x193 y82 z361

I hope this issue is fixed. I know it is not game breaking or anything, but it at least have an impact on player's playthrought. Because I have seen people built a portal underground(especially under y0) and come back to the overworld to find themselves appear from another portal generated by the game usually above ground. This definitely hurt some people play time a bit. For me, I was playing around in the cave and decided to build a portal to get some loot and return to find myself somewhere else that I am not familiar at all. I supposed this bug is not how portal should interact with the new world height extension. Some people's playthrough definitely got interrupt by this bug.

tl;dr: Nether portal built under y0 generated a portal in the nether dimension, but when coming back to the overworld. The portal I appear out off is a new portal generated by the game. And when trying to go back the original portal underground is not connected anymore.

Apologies, if anything is a bit unclear or difficult to understand.

Thank you!