When I scan a group of files that's from a compilation album that MB doesn't know, but the tracks match other albums that MB does know, the tracks end up split off into a bunch of different albums.

When I select all the albums that they matched incorrectly to and try to drag them back to the "Clusters" section of the center pane, it refuses to let me drop them there.  Instead I have to drop them on "Unclustered Files" and then select them all again and then drag them into the "Clusters" section, where they show up (properly) as a single album cluster because the tags already have basic info in them.

I don't understand why it won't let me drag them directly to Clusters without having to go through Unclustered Files first, it looks like it will, but then refuses to let me drop them there, so seems like a bug to me.