Nether portal doesn't fully break when one or more blocks are destroyed

When punching a nether portal block inside of a nether portal frame, the portal blocks did not disappear.

What I expected to happen was...:
for the nether portal blocks to disappear.

What actually happened was...:
Just that one single block was destroyed, but the other parts remained active, and did not disappear.

Steps to Reproduce:
1. Create a nether portal of any size.
2. Enter the nether portal.
3. Attempt to destroy the naturally spawned nether portal by "punching" the nether portal block, not the obsidian.