Comment 6 for bug 1220429

1. I can assure you that it is not caused by a shared routine. All the code implicated in gmb has been written by me, and it's not the kind of code that is sharable, even if quodlibet and gmb where using the same language, which they are not.

2. I cannot speak for quod libet, but as far as gmusicbrowser is concerned, there are 2 distinct problems.
a) a potential bug when saving or loading playlists, they are currently saved as series of numbers referring to their position in the library, it seems there have been bugs in the past causing synchronization problem with these numbers, I do not know if it still happen with current versions.
b) the fact that songs removed from library are removed from saved lists. In gmusicbrowser, songs data are kept for some time after a song is removed from the library, so that if the song is re-added data like labels or rating are not lost. You bug report made me aware that their belonging to a saved list was not lost. It is a tricky problem, and I'm still not sure what I'll do about it.
You can mitigate it somewhat in gmb by un-checking the "Automatically remove current song if not found" and the "Check for updated/deleted songs on startup" in the library tab. And then only "check for songs" or "re-read tags" when you know your device is connected.

3. I can assure you I care very much about all the user's data. In gmb there are 6 complete backups in the ~/.config/gmusicbrowser/, one of the most recent save, the others from each of the last 5 days where gmb has been used.
But bugs happen, and some things are sometime hard to do.

Though in your case, it seems you don't really want lists (that have an order) and simply using labels would work much better, the only problem is that the way to add labels is not as intuitive or convenient as it should be. If you have suggestions on how would be the best way for you to add labels, feel free to share them. Note that in gmb, if you are willing to modify layouts, you can have buttons that add/remove/toggle a specific label to the current song, or checkboxes to change the labels of the current song. I think I'll also add dropping songs on a label in the label list as a way to add labels.