Does this change default to "yes" on unattended installs? I'd assume it doesn't, because that would be dangerous.
EDIT: Indeed, from the same changelog: debian/dash.NEWS.Debian: when upgrading existing installations, the system shell will not be changed automatically (closes:#539363).
Just so we are clear you would be talking about an unattended dist-upgrade from lenny to squeeze? Have you done this?
Please explain how your automated Debian administration system that has been in place since Lenny[^1] handles unattended dist-upgrades without the use of preseeding the debconf database for questions with a priority of high or critical?
[^1]: Squeeze was February 2011, any new stable installation since squeeze defaulted to dash as /bin/sh
EDIT: Nevermind, I answered my own question, unattended dist-upgrades from Lenny to squeeze is not something you have any experience with: "I'm now using Debian Wheezy, after primarily using Windows environments my entire life." https://news.ycombinator.com/item?id=6564610#up_6565766
This is a honest question. How could an automated Debian administration process not be aware of and interact on some level with debconf?