This bug seems to have been open for more than a decade, spanning the entire duration of the last couple of releases. python3-software-properties Recommends unattended-upgrades, which means it gets pulled in automatically on a default desktop install. The debian-installer team stopped installing unattended-upgrades by default as of Buster alpha 4, at the request of the Debian security team (https://lists.debian.org/debian-boot/2018/05/msg00250.html). I don't think it's appropriate for a Python module package (and one that gets pulled in by dependencies from other packages) to pull in unattended-upgrades, even by Recommends or Suggests.
