With kindest regards, Alexander.
Debian - The universal operating system https://www.debian.org
...As an experiment, I've switched apt sources from "deb.debian.org" to "debian.netcologne.de" and everything went back to normal.
But 8.14.1-2+deb13u2 is currently in
http://deb.debian.org/debian trixie/main amd64 Packages
So I still suspect either stale mirror or update during interval between sync of proposed-updates and main trixie section.
I will pin everything from "trixie-proposed-updates" to lower priority, so packages from this source won't be considered as candidates.
And wait long enough to get candidate versions from "stable-updates".
Probably it is good idea to report somewhere about this issue, so it gets a proper fix.
A note on possible interference of backports and proposed updates may be added to <https://wiki.debian.org/StableProposedUpdates> and linked from <https://wiki.debian.org/Backports>. Either I missed something or what you faced should not be a frequent accident. Perhaps there is a more plausible chance to get unsolicited packages from backports if proposed-updates are disabled after single upgrade from proposed updates. Pinning of upgraded packages may be required. Removing of packages from proposed-updates without their migration either to updates or to stable sounds like something exceptional. Your list is rather long.