So if you create a nether portal, it creates one linked in the nether, if you create another portal within 128 256 128, the nether portal will take you to the first and closest portal, which is going to be the first one. If i understood the forums correctly this process of un-linking portals is broken in some way. I created two portals in the over world both are within the 128 256 128 range, when i destroy the first portal created, the nether portal does not instead link to the second one, it creates a new portal within the area of the first portal. In the picture provided it may help clarify what i'm describing. In the overworld there are 2 portals within 128 256 128 and they are both linked to one in the nether, if you break one of the portals in the overworld, the nether portal does not link to the second portal created (The closest one), it instead generates a new portal within the first nether portals area and this allows for infinite obsidian generation as well as much annoyance. This video may help explain it further https://www.youtube.com/watch?v=vwCXm4Gq0Wg