Odd portal bug

So I started a new map to try this mod out and built a small underground base, got the supplies for a nether portal and put it in a room across the hall from where I put my aether portal once I got the glowstone. Once I got into the aether I was in the middle of the sky so I made a dirt bridge to the nearest island and made another portal there, which went back to the one in my base as well. So then I went and broke the first portal in the aether that was floating in the sky and everything was running smooth.

A bit later I found a gold dungeon and fought the boss and promptly died, then got respawned back in my base in the normal world. So I went back into the Aether and saw some moas and colored sheep which I had yet to see spawn so I decided to head back to my regular world base to get a sword and some shears to deal with them. When I went back into my portal this time though it created another portal away from my base up on the surface. After walking back to my base and trying to go through the portals again it dropped me back out into the wilderness every time. So I tore down the new portal it had created it and walked back and retested them again and it works how I originally had it set up again. Not a huge issue, especially since I got some free glowstone, seemed like something wasn't working properly though.

If it's helpful at all my underground base's portal was at X: 23, Y: 57, Z: 54, the portal that got created after the dungeon boss killed me was at X: -70, Y: 74, Z: -125.

Nether and Aether portals use the same creation mechanics and this doesn't sound like anything that out of the ordinary as far as Nether portals go, I think I've heard the same thing somewhere else.

In other words

more likely a bug with the portal mechanic itself rather than the mod