Smart playlists causing my iPod to be restored

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I've had this problem since about half way thorugh last year, I think it was after upadting to iTunes 11 but i can't be certain. Anyways whenever I create a smart playlist then eject my iPod all my songs dissapear and my iPod restores itself. Over the past month I haven't used a smart playlist but today the moment I created a smart playlist as soon as I ejected my iPod everything was gone. I've updated the iPod firmware to latest version and likewise with iTunes and I've searched various forums to no avail. Please help!