Syncing ipod with rhythm-box

I have installed Rhythm Box on my computer (which is now running on ubuntu) and I really like the programme. I've managed to copy the music off my pod onto Rhythm Box, but whenever I try to copy music off the library back onto the pod the programme seems to shut down immediately and then when I open it again, the music I'd deleted off the pod is back on there. There doesn't seem to be an obvious 'sync' button, so I wondered if any of you Ubuntu gurus out there could help? thanks!