Like Joel, I'm guessing you have this iPod synced to another computer. If you switch between two computers with your iPod, this 'update' will always happen. The only way to harmoniously sync the two would be to update your songs on the iPod manually, which requires you to drag specific songs/albums/artists into your iPod rather than having them in a nice organized playlist. To change this, go to the 'Preferences' menu of iTunes, and you will see this 'manually update songs' option under the 'iPod' section.