The following is a potential partial workaround for this problem.
Note, however, that this method was attempted on MAC OS X, not Windows; therefore, though both versions of iTunes are assumed to be essentially identical in appearance and function, it is possible that this method will not work for WIN users.
Also, be aware that this is NOT a fix for the larger sync problem, but it should allow you to continue adding new music to your iPod Classic.
1) Download and/or import the new music you want to add to your iPod into iTunes.
2) Connect your iPod, and click on the iPod icon when it appears at upper left on the main iTunes screen.
3) Under the "Summary" heading in the sidebar, look for the "Manually Manage Music" option on the Summary page, and make sure the box for that option is ticked.
4) Go to your library, select (highlight) the new items you just imported, and drag/drop them to the iPod icon. Make sure the icon outlines in BLUE before you drop the items.
You should then see that iTunes will begin loading the new items to your iPod.
You should not have to check the "Manually Manage" setting every time you connect your iPod; however, if for some reason the setting doesn't stick, you will know because iTunes will no longer allow you to drag/drop items to the iPod icon. In that case, you would have to go back to the "Summary" section and re-check the setting box. In the case that Apple actually addresses this bug, you will likely have to uncheck the "Manually Manage" setting in order to return to an automatic sync.
Again, this method does not supplant a full automatic sync, but it should allow you to keep adding new music until Apple fixes the problem.
