Random extra Nether Portal was generated, & now I can't go back to my 1st Portal.

What I expected to happen was...:
I made a Nether Portal (A) in my Base, & went to the Nether.  Later, I used the Nether Portal (B) IN the Nether to, presumably, go back to A (the only other Portal there should've been) in my Base.

What actually happened was...:
I returned to the Overworld, but not via A.  I arrived about half a minute's run from my Base (where A is), where it generated an extra Nether Portal (C)!  I experimented, & A goes to B, but B & C go back & forth to & from each other.  I cannot use B to go back to A!  I even removed a block of obsidian from C, deactivating it.  But when I went A to B, then used B, it generated another Nether Portal (D), 2 blocks away from C!  Now B & D are connected, & I still can't go from B to A!  What the hell is going on?!

Steps to Reproduce:
1. Make Nether Portal A (in the Overworld).
2. Use A to travel to Nether Portal B (in the Nether).
3. Use B.
4. Instead of A, arrive 1/2 minute's run from A, at randomly-generated Nether Portal C!
5. Remove obsidian block from B (deactivating the portal).
6. Use A to travel to B.
7. Use B.
8. Instead of A, arrive 1/2 minutes' run from A, at randomly-generated Nether Portal D (2 blocks away from C)!

I doubt anyone will be able to reproduce this bug, but I still want to know what the hell is going on!  I just want B to link back to A!  Help!