[Zubersoft]

That will not work. Source Type is a completely separate field like "Key". All you did in that example is change what the search text will check against and then filtered on songs that don't have a source type unassigned. You can't currently search for any song that does not have a value in the custom 2 field. There is no support for that. The "unassigned" filter only applies to the group types, i.e. collection, album, genre, source type, key, year, custom group, etc. You could rename the "Custom Group" field and use that instead of custom 2, and that would work for what you are trying to do.

Mike