If there is a generated portal in the nether connecting to your overworld portal, if you break that overworld portal while entering, the game will teleport you somewhere else in the nether without a portal

As stated in the title, if you break a portal as you enter the nether, no portal will appear.

How to recreate
1. Set up a nether portal
2. Enter the nether, generating a portal
3. Go back through to the overworld
4. Break an obsidian block that creates the portal as you enter
6. You will get spawned somewhere else in the nether without a portal