I'm using Ubuntu 11.10.  It looks like, after a banshee update on 10/20/11, a lot of the songs in my collection suddenly became "recently added," and because they had been lost and re-added to the database, those songs now no longer appear in the various playlists that I have put together over time.  Not a huge problem, but it causes a bit of inconvenience to have to re-add songs when I find them missing from a playlist I like.

The songs that this happened to appear to all be ones with one or more of the following characters in the title, artist, or album name: & ( ) ,
I'm not sure if it's having these non-alphanumeric characters in the metadata or the actual file/folder name that's the problem.  It doesn't seem to be all the songs with these characters that were lost and re-added though, only a subset of them.

I'm not sure if this is just a one-time thing that was caused by a particular change in Banshee 2.2.0.  It seems like the new version may have changed the way the database handles tracks with unusual characters, and in the process of "updating" to the newest version of the database, these tracks were temporarily "forgotten".  It would be nice if the upgrade could happen without losing track of music that has already existed in the database for a long time.