Pardon me if I'm misunderstanding you, but if I'm recalling correctly, the album art viewer in the Default UI only shows artwork during playback or when you're actively selecting tracks.If that isn't what you're talking about, I suggest that you provide more detail about your foobar configuration.
I think that's unreasonable, yes. Most people have more than 1 album in a playlist. And what if the platlist is long and the currently playing tracks are out of view? Visiblity of items shouldn't be related to whether you can see their album art (well, except if you're using a playlist componet that supports inline art display, obviously )What is reasonable, I think, is that Foobar doesn't immediately forget everything after playback stops, and thus might continue to display relevant data about the last played item.