I'm using a new Mac Mini with OSX 10.8.3, and a retina iPad with the Spotify app.
There are 4 local files both on the desktop and the iPad which are used in Spotify playlists. On the desktop they show up and play without any problem whatsoever.
On the iPad, even though all the files are on the iPad's own local hard drive, they are completely absent from the playlist. They are not included at all - it's as if they were never added in the first place. I have not seen any one else report this specific problem - they all say they can see the songs in the list, but they are unplayable.
I have followed all the steps listed here - added the songs to the playlist via the desktop machine, made the playlist available offline via the desktop machine, then, using the iPad connected to the same WiFi network, set the same playlists to download/available offline, but since the songs don't even show up as part of the playlist on the iPad app, they don't download to the iPad (which is pretty redundant, since the files are actually present on the iPad harddrive already - I manually moved them there via iTunes so Spotify would be able to utilize them, but apparently that's not how it works).
I can even see my iPad in "Devices" in the Spotify sidebar, so I opened it from there and synced the playlists in question. It still acts as if the local songs are not even part of the playlists and skips over them.
I don't want to ask a question that's already been answered, but every other post seems to specify that A: the files are only stored locally on the desktop (mine are stored on the iPad already, but still don't show up) and B: they can at least see those songs in the playlist via their mobile device, they just don't play (on my mobile device, the songs are not even present as part of the playlist).
Would appreciate any help, as we were building our wedding reception's music around Spotify's iPad app, and are running into this bug very close to the wire. Some of the songs were even previously available on Spotify (when we first added them to the playlist) and have since been removed, which is another huge headache.