I made a nether portal in the overworld,(portalA) lit it up and then created a copy of the same world on creative, to first check the nether spawn for any potential dangers. I spawned in a small cave (in the nether) (portalB) near a lava ocean and went back through the same portal. i ended up on a mountain approximately 100 blocks away (portalC). I then broke the portal. (I know this happens if the portal in the nether cannot be placed at the ideal coordinates.) Then I went to the nether on my survival world. I went through the exact same nether portal (portalA) and was expecting to come out in the same cave. Instead, the loading screen for the nether (netherrack background) just changed to loading screen for overworld (dirt background). When I came out, I was in an overworld cave (portalD), approximately 100 blocks away, not in the same location as on the creative world.

I think that going through the same nether portals on two identical copies of the same world should result in exiting through the same portal as well.

While I was getting coordinates of portals for this bug report, another problem occured to me. I was trying to get coordinates of the nether side portal (portalB) on creative, so I went through. I stepped out of the portal, everything looked normal and after a few seconds, I was placed back in to the portal, like I was stepping out again. (I have previously experienced being placed back into the portal and exiting again and thought it happened because of lag) Then it teleported me back to the overworld (portalA). The same thing happened, when I tried again. When I went through for the third time nothing unusual happened. (maybe because I waited in the portal for a second before stepping out) Going back to the overworld, everything went fine. This time I went back through the original portal (portalA).

seed: 1883875724119310463

coordinates:

original portal in the overworld: 150 66 36 (A)

nether side portal on creative: 3 24 7 (B)

exit portal on creative: 15 136 56 (C)

exit portal on survival: 15 95 -33 (D)