Nether portals that are /setblock in the End do not teleport you to the Nether, unlike Java Edition

I don't know for sure, but the part about going to the end sounds like the portal teleports you to the overworld based on dimid notequal 0 (overworld), not dimid equal -1 (nether). The portal probably generated around the location you spawned in, try repeating with Night Vision?

I can confirm this. I actually found this bug by playing around, and when done correctly, teleports you to the overworld at 0, 32627, 0, and end portals dont teleport you and nether portals do the teleporting animation indefinitely without teleporting you. Here's proof: Weird Minecraft Bug - YouTube

Edit: I'd try to reproduce this without using the add-on, but Minecraft won't download right now

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