The nether portal (in the nether) seems to not be linked to the parent one I've created in the overworld. Every single time I've tried to correct this problem, it seems to create a new portal. I'm not sure why this happened, I've even tried clearing obstructions from the portal but I still get warped to a different location every time.
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Works as intended, see MC-1403.
What are the coordinates of the portal in the overworld and what are the coordinates of the portal you wanted to create in the Nether?