Hi Dan, thanks for your bug report. Indeed there’s a bug in version 8.0.x in maintainer scripts regarding the alternatives handling. The preinst is not correctly removing alternatives for files we don’t ship anymore and that produces the errors logs you described. I’ve been working on the desktop-base package for Stretch and I ensured we don’t have the same problem for the upgrade from 8.0.x to 9.0.x, so I’ll mark this bug closed with the next upload.
As for Jessie I don’t think a fix is worth the effort, as the messages are mainly warning and in the end update-alternatives automatically removes the alternatives pointing to non-existing files or folders. Cheers, --Aurélien
