ok, a little more investigating:
looks like both problems are related to the number of added tracks in a playlist. if you try to add more than 450-500 tracks to a playlist, you encounter this problem. no error message is reported, so you may not know you didn't add everything that was attempted. after this, it is no longer possible to add anything to any playlist, or add to a new playlist without a restart. tracks are added fine to playlists if you keep it under 450. my work around was to break my collection down into smaller chunks, add these chunks to my library, then add these chunks to the playlist, then remove the chunk from the library and move on to the next. needless to say, this is tedious, but works. i eventually lost patience and just created a couple of lists on amarok, and copied the m3u to the .mediabox directory, which works fine. anyways, a couple of suggestions/requests:
1. is this limit built into mb, or is it a bug? if the former, is there a workaround to remove it? i think that most people have more than 500 tracks in their collection if they use the nokia for music.
2. in future versions, is there a way to speed up loading of the lists? maybe make it selectable whether to create a preview/load thumbnails or not, or just be able to play the playlist directly without first loading it?