I've noticed that Picard keeps downloading track data after I have already deleted the loading albums (or all albums) from the right hand pane.  The status bar at the bottom shows a slowly decreasing number next to the down arrow icon, but all those requests are useless and unused, and just creates unnecessary load for the local computer as well as MB servers.

This is most obvious (and painful) when I scan compilation albums where the tracks scan and match to other very large compilation albums.  In some cases I end up with over a thousand tracks downloading when I only have a dozen or so tracks.  As soon as they all are in the right pane, I select them all and move them to the "right" album, and then delete the other compilation albums that are still loading, but after those are deleted picard continues slowly downloading the track data for all those deleted tracks.