Steps to Reproduce:

1. Create a Nether Portal in the Overworld and enter it to load the Nether.
2. Exit the Nether and build a Nether Portal less than 1000 blocks away.
3. Enter the new Nether Portal.

Observed Results:

The new Nether Portal will take you to the same location as the old Nether Portal.

Upon reentering the portal from the Nether you will be taken back to the same location of the old Nether Portal in the Overworld.

Expected Result:

The new Nether Portal should create a new portal in the Nether, and should take you back to the new portal’s location in the Overworld upon reentering it from the Nether.

Side Notes: 

• Occasionally this bug will also take place if the new Nether Portal is built more than 1000 blocks away from the old one.