Ok first off, this bug might be "seed" specific, this is the only seed I've encountered this bug on so far.

Seed "-4294155304399390074"
Survival, Cheats on, Structures on, default world type.

You will begin near XYZ -264 / 68 / 229

I set up my base camp in this area and I had created my nether portal in this general area. When you enter, it will put you right next to a nether fortress. Mine put me right on top of it actually. Anyways I felt lucky to be so close to a fortress without having to hunt for it. However, when I got what I needed and left, the portal took me back to the main world and I was lost. It took me back to coordinates XYZ -284 / 73 / 61 (general area). This was the first time this has ever happened to me. Curious, I created another world with the same seed and went to the area to see if perhaps a portal had already existed for some odd reason. But there was nothing there. Any idea why this is happening or how to fix it so the portal brings me back to the one I created instead of this unusual one about 160 blocks off on the Z coordinate. Luckily it's still somewhat close so it's not a huge inconvenience.