It has now happened the other way. My game crashed as I was about to enter the portal in the nether. When i reloaded I was at the portal. Went through and it spat me out at the same overworld coordinates as the nether portal with no portal. I closed app, reloaded and was at the same overworld coords but now with an active portal half buried in the ground. Went through and was at a different nether biome. Ended up dying and loosing all my stuff again trying to shortcut my way home through the nether as the above world coordinates were forever away from my base. I'm so annoyed. It's only happened twice, but both times have been at crucial moments for me. Can't wait for this to be fixed.
I had a similar issue but a bit different I think. It has never happened until after the latest update. Used my usual portal at my base that I have been in and out of many many times, however I was spawned on the otherside of the underworld with no portal, and coordinates did not match my above world portal either. I didn't eat as I went through. When I eventually died and went back through, everything was as normal. I have since used it about three or four times and so far no problems. Was a random section of underworld I hadn't explored and even after almost an hour of travelling back towards my original portal coords, i was still thousands of blocks away. This was on playstation. Hope this info helps. Also my world is 360MB total.
Mine is single player