Nether portal glitch

Put the summary of the bug you're having here
When we go to a spot to build a nether portal and it keeps putting use on a island in the middle of the lava ocean and we went back to the portal and then went 1000 blocks away from the original portal and build a new one and it did the same thing except it took you through one where the original was
What I expected to happen was...: a different place
Describe what you thought should happen here
Take you to a different place in the nether
What actually happened was...: it took you the same spot where the original was
Describe what happened here

Steps to Reproduce:
1. Build a portal and go through it and look at your surroundings
2. Go back out and head 1000 blocks away from the original portal and build a new one
3. Go through it and it will be the same