Playing in 1.7.4, a Ghast hit my portal. It didn't break it/extinguish it, like normal. It deactivated the bottom half. Could not re-light it or deactivate top half manually.
I tried using Flint&Steel to re-light the bottom, tried deactivating the top portion, tried using various weapons/tools to break it. Walking into the portal did nothing. But I was able to place a block of dirt in the bottom of the portal, stand on it and get my head into the top activated part enough to send me home.

Forgive me if it's frowned upon, but here it happened to happen during my weekly series so I have video of all of this too:
http://youtu.be/Ey0st2q_9N8?t=13m29s (I set it to start right when it happens)