A way to fix this would be to disable shared libraries entirely, then rewrite the default storage path for music and other media in iTunes to the directory of your NAS drive. Worked for me.

1. Open iTunes > Edit > Preferences
2. Go to "Parental Control" and under "Disable" check "Shared Libraries"
3. Go to "Advanced" and change the location of the media folder to your network path.
Now depending how you have the drive set up it may try to reorganize everything, the process may take a while so grab a snack and watch TV.