Nether portal Bug

Put the summary of the bug you're having here

What I expected to happen was...:
When the ghast fireballed my nether portal back to the overworld, i expected it to disable the portal

What actually happened was...:
The portal deactivated but the final 2 portal blocks were still active and i could still go back to the overworld

I didnt pay attention on how to produce the bug because i was focusing on something else.