I reset the settings. Still, using v0.7.0, the problem appears when I drag an artist or album name from the collection into the playlist to add all tracks at once. I get many greyed out song names then and the files can't be found. Can't really make out a pattern, as some files of an album will add fine and others with the same encoding won't.
Opening every album seperately with the arrow icons and dragging the songs directly into the playlist mostly works.
Dragging the mouse to "local" when adding to the playlist seems to work better, although it will still fail to add some albums, but I don't get all the greyed out entries (I think many of these are from automatic online sources, even though I don't have any online sources configured). The behaviour is definitely weird.