This is fairly difficult to explain but, I decided to create a Nether portal but realised that it was not a good location it sent me to. So I deconstructed it and set up another one a hundred blocks or so away. When I got into the Nether, I realised it was the same spawn point as last time. I went back into the over world only to notice I ended up in the place I put my first portal even though I deconstructed it and placed a new one somewhere else. This gave me duplicate portals and if destroyed, duplicate obsidian.

Device is Huawei Y7