Didn't that only happen once, with season 3?
I thought it happened with season 1 and 2, as well?
Nope, it only happened with season 3. As you can see from TV.com and IMDB.
And this isn't season 4 pt 2, but season 5. But the writer's strike only affected this season by when it was going to air. If there wasn't one, then it would have aired this summer. Since it did happen, it got pushed to the fall.
By the way, how many season does everyone think are left? I have to go with at least two more.