iTunes Issues syncing to iPod Touch

Hello,
I've recently been having a problem with syncing music to my iPod Touch (running iOS 5.0.1) with iTunes 10.5.3. My Mac is running Lion 10.7.3. My problem is that iTunes is not re-syncing my music to my iPod when the file changes on my computer. Say for example that I change the metadata (adding a new cover art or something like that). In this case, the copy on the iPod does not get updated with the latest changes on the Mac. In order to get it to re-sync, I have to remove the updated music files from my iPod and re-add it. I am not using the "manually manage music" feature, but am using regular syncing (using a series of master playlists that I manually update to choose what content to load onto the iPod as I manage multiple iPods from one master iTunes library). Has anyone run into anything like this before? If so, what is the fix (if there is one)?

Regards,
Geoffrey