That's what I would have assumed.  What about the opposite -- if I remove a folder from the list but then I see that all the tracks are still there. Would I have to go through and manually hide the tracks I wanted removed? That seems like a major pain.

Right now when a user removes a folder, is there any sort of popup confirmation?  That could be a place where we could add a checkbox (default on) saying "hide tracks from this folder from the library."

In general mixxx has a "no delete" policy, so as long as we're consistent I don't think there will be confusion.