A new unnecessary nether portal is created in the overworld when returning from the Nether

This is a large-ish map that I started playing with 1.13.2 and I am now playing the same map with 1.14.

I have a nether portal in the OW at or about (892, 63, -234). I entered the nether here. I ended up in the nether at (151, 70, -67). I have done this several times. Whenever I go back to the OW (even after just a few seconds), I end up at a automatically-generated nether portal at (1209, 70, -520). It is above open ocean. This behavior is new with 1.14.

I had a nether portal near here the second location (about 80 blocks away) that I took apart, but that was several weeks ago.

I can include a tgz-ed version of this map data if it will help. (Let me know which directories to include.) When I upgraded the map, I let it make a backup. I can supply that if it will help. Let me know.