Joe's dashboard

I recently upgraded my 1st Gen iPhone to 3GS. I FINALLY can access iTunes on my iPhone and all seemed right with the world. My first attempt at downloading from the iPhone as opposed to iTunes on my PC at home was succesful. When I connected my iPhonto my pc at home, all went as planned and newly purchased music (downloaded on my iPhone) transferred over to my iTunes account.
It had been a while since re-synching my iPhone and there is a lot of music that needs to be dumped to iTunes. Last night I attempted to synch my iPhone with iTunes. Everything but the music transferred without incident. I can not seem to get all the newly purchased music to transfer from my iPhone to my iTunes account. When I hook up my regular iPod nano to my PC. everything transfers if I had downloaded music from my iTunes account at the office. Does anyone have any idea why this may be occuring ??