If the "Multiple Items In Tags" field is modified, current playlists are cleared, and a "Clear library and rescan everything" is performed as oppose to the specified "start a rescan of your music library". (To me that implied "Look for new and changed music" (gentle - faster) rescan.)

If a complete library clearing is necessary, can it done at a later time, at a listener's choosing rather than stopping everything? BIG BOLD letters could be added in the description to let the user know that the changes will not take affect until a complete rescan occurs.