After doing an offline install of i386 from a server CD, /etc/apt/sources.list has the CD commented out. It also has the Ubuntu archive in /etc/apt/sources.list present and uncommented (though I'm unsure if that is a bug or not). Manually adding the cdrom with apt-cdrom scan works, and allows packages to be installed, as well as tasks.
Steps to Reproduce:
1. Install i386 ubuntu normall
2. cat /etc/apt/sources.list, see the CDROM is commentedout
1. The CD will be automatically polled if internet sources can't be reached or updated.