If your Nether portal is larger in the Nether than the one in the Overworld, and you enter the portal from the Nether from the portal's edge, you will spawn in the Overworld inside the Nether portal's frame and suffocate.

What I expected to happen was...:
I would enter the Nether portal like normal and continue my projects.

What actually happened was...:
I entered the Nether portal, and started to suffocate on the other side.

Steps to Reproduce:
1. Make a Nether portal both in the nether and the Overworld, and link them
2. Make sure that the Nether portal in the Nether is larger than the one in the Overworld (in this case, my Nether portal in the Nether was 7x7 and the one in the Overworld was 5x5)
3. Enter the portal in the Nether through the very edge. You should spawn in the portal frame in the Overworld, and suffocate.

Here is a link to show what happened: https://youtu.be/JgTvW9-ZntE