I'm exeriencing the same problem and want to counter the argument that it's a good incentive to correct the apt configuration.
I allways have backports PPA configured to have current packages in latest (ubuntu) stable release. At the release time of a new stable, the backports repositories are not populated (yet), but I keep them pointing to the new version of the repo so that when developers start populating the repo I will instantly enjoy the update without having to think about adding the repo back. This has allways worked, until now. Although the work-around (quit/restart aptitude) is not a big problem I just wanted to add a (in my opinion) valid usecase of maintaining invalid repository configuration that should preferably be ignored gracefully. Best regards, Martin
