I'm not sure how many replies I'll get here, because it could be quite a niche example of stupidity. But anyway...
For years, until quite recently, I thought that Send In the Clowns was the name of that jolly barrel organ-type tune that they used to play in circuses when, well, the clowns came out. It was only a couple of years ago that I found out that Send In the Clowns was a melancholy show tune about missed opportunities and lost love, and the jolly circus music is actually a classical piece called Entry of the Gladiators.
Has anyone ever laboured under a similar misunderstanding, or is it just me?