After adding frozen sources to /etc/apt/sources.list and doing apt-get update, apt-get dist-upgrade reports an error similar to what's cited in this bug report and refuses to do anything after downloading a slew of packages. The literal text I'm seeing is: E: Internal Error, Couldn't configure a pre-depend with no other hint as to what needs to be done to address it. This is in trying to take an up-to-date stable machine to the frozen branch.