Agreed.
That was my only annoyance after the upgrade from 6.06 to 6.10 so far. Even things like pushd/popd don't work in dash.
Changing the default shell to something which does less is a huge modification.
When running a dist upgrade, this issue should have been presented to the user with the possibility to opt-out and keep the old default shell.
Besides that I had a very smooth transition from 6.06 to 6.10. Note that I had my software RAID grub boot item outside of the DEBIAN AUTOMAGIC KERNELS LIST. That saved it from being touched by the upgrade process. Phew.