I'm not sure if this is an intentional feature, but I can't find anything describing something similar online.
I built a portal several blocks lower on the Y axis than an enchantment table (three blocks total between the two; so, from lower Y to upper Y, it went portal, one block of air, one block of polished diorite, then enchantment table) and whenever I traveled through it to the Nether, my character would catch fire.
The enchantment table was on a room/ platform (complete with bookcases surrounding) built above naturally generated dirt ground. Underneath the platform on the ground was the portal, set about two blocks deep into a small pit dug into the dirt
I experienced another common error with this portal, where the portal connects to another existing set in the Nether. It was also catching me fire at this point. I traveled to where the portal should have been coming out in the Nether and built an exit portal there, which connected properly, but I was still catching fire. I tried digging out around the portals (both in the Nether and the Overworld), but couldn't find any lava or netherrack on fire nearby. I tried destroying them both and rebuilding them in the same place, no effect. I moved the one in the Nether a ways away, no effect. When I moved the one in the Overworld away from the enchantment table (probably about 20 blocks or so) it fixed the problem, so the only thing I could think that might be the cause was the enchantment table, but of course that's only a guess.
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@KJP12 No, as I said, I do not believe that was the cause in this case. I looked all around each side of the portal (Nether and Overworld) and there was no lava or anything on fire. It was consistent and didn't happen just the once, and I was the only player online, so it wasn't random happenstance like a zombie on fire walking by either.
The "other" coordinates in the Nether could potentially be very far from the actual exit portal - if you went from an Overworld portal at 800,y,800, it would briefly put you at 800,y,800 in the Nether (which could contain fire or lava) before teleporting you to the portal closest to 100,y,100.
well, this is not really MC-98153 to be honest
So for clarity, an anti-cheat function in the game is first placing me in identical Nether coordinates, before dividing by 8 and then putting me in the final Nether location? And those identical coords contain fire/lava, so if I wanted to fix this I could go over there, remove the fire/lava, and all would be well? That's doable of course but I sure hope a patch is being worked on for that. Bothersome and obviously not what's expected from the player's side.
This is caused by the player being teleported to the nether at coordinates divided by 8 then back to original pos and back. And at the original pos, there is a fire or a lava spill there.