Problem with Caching Songs - moving from online to offline mode

I've been using U1 music as my sole music player for a number of weeks now, and given that I get on and off the london underground I've been going a lot from online to offline mode.

The problems that I've been facing is that if I start to play an album (for the first time) and it's streaming on 3G, then I go out of service, it caches that song and sometimes the next song. However, when I'm next back in service, be it wifi or 3G, that same album with only play up to the point where it cached last time, it won't progress any further, and I can't even select songs further down the album's playlist, it just stops where I got to the first time I was playing and went offline.