I'm not sure, but I don't believe the episode "Old Folks at Home" has a single misunderstanding in it.

And it's the only one I can think of without any. Are there others?

I don't think "Jack the Ripper" had any misunderstandings. It was just Jack and Mr. Furley trying to be more agressive people. :)

Actually, both the episodes with Dr. Prescott seem misunderstanding-free. "The Root of All Evil" also. Hmmm... is that why they needed a shrink? ;)