Backported libp11-kit0 (for gnutls28 for vlc backport) breaks gnome-keyring at least for libvirt-bin.
Symptoms: libvirt-bin emits error message about p11-kit config file and gnome-keyring and fails to start.
I didn't bother trying to run the system without libvirt to see of gnome-keyring breakage only affected libvirt because my interest was in running a VM.
I had upgraded to backport of vlc (and dependencies) because of Iceweasel/firefox reporting vlc plugin insecure and out of date (ironically update vlc does not update the plugin so I was also no further ahead on the mozilla plugin).
Regards,
Daniel