Spotify Mobile:0.4.12.180 (but it's been there since at least 0.4.04)
When in offline mode, local files are greyed out but can still be played. This makes it tricky to work out which are local files and which are not.
Here are some screenshots to illustrate what I mean. Apologises for the poor quality, I had to turn the flash off.
Main Playlist screen:
Hopefully you can see all playlists are greyed out. The second, third and fourth playlists only contain local MP3s but are greyed out just like the playlists that haven't been configured for "offline mode" (i.e - the rest of the playlists in this screenshot).
The top one is Rihanna, here is the Rihanna album:
You can see it's white and not greyed out but nothing indicates this from the previous screen.
Yes it would if I selected this album for "offline mode" but it only contains local MP3s. So A: Why would I bother? B: Surely this doesn't mean I've got to set every album with local MP3s to "offline mode"? I've got thousands.
This isn't specific to playlists containing local files. It affects all playlists you haven't specifically made available offline. For example, if you create two playlists containing the same tracks and make one of them available offline, Spotify will only show the playlist you made available offline as available in offline mode and the other will be greyed out.
Playlists containing local tracks automatically found by Spotify on your phone would seem to be the same thing. You haven't specifically made the track available offline and so Spotify treats it as not available. Once you open the playlist it can tell that the tracks are available and they aren't greyed out.
If a playlist only contains local files obviously it's available offline. Spotify should be able to work this out. I shouldn't have to set each playlst as offline, if all it contains is local files. I've got my Windows Media Player playlists imported, so have hundreds too.