Nether portal creating random overworld portal underground upon exiting the nether.

This has happened to me in every new world I've created so far, even before the newest update. Upon making my first nether portal and entering the nether, it always spawns me under a lava lake without fail. When I exit the nether through that same portal it does not put me back through my original portal but instead creates a whole new portal in a random cave far underground. I've tried breaking that newly created portal, returning to my original one, going through to the nether and back but it just keeps putting me in newly generated overworld portals somewhere underground. I have attached screenshots of my first and only nether portal by my base, my nether portal in the actual nether and the third portal that keeps on being created in a cave after existing the nether.