It is important to note that in this edition, the updates from Debian are frozen via the update packs (new linuxmint repo). However, the updates from the security and multimedia repo have not been frozen - and as such are not compatible with the main Debian repo.
Because of this It is advised not to update the system if you choose to install from the new iso's.
The security and multimedia repo's will be frozen when update pack 3 is integrated and all sources should point to Mint.
EDIT: Please read the information provided in the release announcement -> http://blog.linuxmint.com/?p=1818
This release comes with Update Pack 2 and points to the “Linux Mint Debian Latest” repository as well as the Debian “Security” and “Multimedia” repositories.
Starting with Update Pack 3, “Security” and “Multimedia” become part of “Linux Mint Debian Latest”. When Update Pack 3 is made available, your sources will need to change and all of them will then point at Linux Mint. In the meantime, it is recommended not to apply updates coming from “Security” and “Multimedia”, as they might not be compatible with the packages in Update Pack 2.