Nether Portals in the overworld all end up in one location

I created a nether portal (portal 1) in one location away from the main area I want to work in and then created another (portal 2) in a separate area.

Upon entering portal 2 it linked with portal 1. I destroyed portal 1 and then travelled back to portal 2 in the overworld.

I then entered portal 2 again and tried to return to the overworld but instead of taking me to the overworld location of portal 2 the game spawned me at an entirely new portal that was within the approximate area that I had made portal 1, even though portal 1 no longer existed.

Is this a bug or part of the game design? And how can I overcome it?