Install sequence (broken into pieces) that leaves the state files in place bug the service still disabled and not started.

ubuntu@i-kvm:~$ sudo dpkg --ignore-depends=qemu-block-extra --purge qemu-block-extra
(Reading database ... 48533 files and directories currently installed.)
Removing qemu-block-extra (1:6.0+dfsg-1~ubuntu1~impishppa20) ...
Purging configuration files for qemu-block-extra (1:6.0+dfsg-1~ubuntu1~impishppa20) ...
Failed to stop run-qemu.mount: Unit run-qemu.mount not loaded.
ubuntu@i-kvm:~$ ll /etc/systemd/system/multi-user.target.wants/run-qemu.mount /var/lib/systemd/deb-systemd-helper-enabled/run-qemu.mount.dsh-also /var/lib/systemd/deb-systemd-helper-enabled/multi-user.target.wants/run-qemu.mount; systemctl status run-qemu.mount
ls: cannot access '/etc/systemd/system/multi-user.target.wants/run-qemu.mount': No such file or directory
ls: cannot access '/var/lib/systemd/deb-systemd-helper-enabled/run-qemu.mount.dsh-also': No such file or directory
ls: cannot access '/var/lib/systemd/deb-systemd-helper-enabled/multi-user.target.wants/run-qemu.mount': No such file or directory
Unit run-qemu.mount could not be found.
ubuntu@i-kvm:~$ sudo dpkg --ignore-depends=qemu-block-extra --unpack qemu-block-extra_1%3a6.0+dfsg-1~ubuntu1~impishppa20_amd64.deb
Selecting previously unselected package qemu-block-extra.
(Reading database ... 48525 files and directories currently installed.)
Preparing to unpack qemu-block-extra_1%3a6.0+dfsg-1~ubuntu1~impishppa20_amd64.deb ...
Unpacking qemu-block-extra (1:6.0+dfsg-1~ubuntu1~impishppa20) ...
ubuntu@i-kvm:~$ ll /etc/systemd/system/multi-user.target.wants/run-qemu.mount /var/lib/systemd/deb-systemd-helper-enabled/run-qemu.mount.dsh-also /var/lib/systemd/deb-systemd-helper-enabled/multi-user.target.wants/run-qemu.mount; systemctl status run-qemu.mount
ls: cannot access '/etc/systemd/system/multi-user.target.wants/run-qemu.mount': No such file or directory
ls: cannot access '/var/lib/systemd/deb-systemd-helper-enabled/run-qemu.mount.dsh-also': No such file or directory
ls: cannot access '/var/lib/systemd/deb-systemd-helper-enabled/multi-user.target.wants/run-qemu.mount': No such file or directory
○ run-qemu.mount - Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there
     Loaded: loaded (/lib/systemd/system/run-qemu.mount; disabled; vendor preset: enabled)
     Active: inactive (dead)
      Where: /run/qemu
       What: tmpfs

Jun 23 09:47:38 i-kvm systemd[1]: Mounting Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there...
Jun 23 09:47:38 i-kvm systemd[1]: Mounted Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there.
Jun 23 09:50:09 i-kvm systemd[1]: Unmounting /run/qemu...
Jun 23 09:50:09 i-kvm systemd[1]: run-qemu.mount: Deactivated successfully.
Jun 23 09:50:09 i-kvm systemd[1]: Unmounted /run/qemu.
Jun 24 09:40:31 i-kvm systemd[1]: Mounting Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there...
Jun 24 09:40:31 i-kvm systemd[1]: Mounted Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there.
Jun 24 09:45:36 i-kvm systemd[1]: Unmounting Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there...
Jun 24 09:45:36 i-kvm systemd[1]: run-qemu.mount: Deactivated successfully.
Jun 24 09:45:36 i-kvm systemd[1]: Unmounted Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there.
ubuntu@i-kvm:~$ sudo DPKG_MAINTSCRIPT_PACKAGE=qemu-block-extra /var/lib/dpkg/info/qemu-block-extra.postinst configure 1:6.0+dfsg-1~ubuntu1~impishppa20
run-qemu.mount is a disabled or a static unit, not starting it.
ubuntu@i-kvm:~$ ll /etc/systemd/system/multi-user.target.wants/run-qemu.mount /var/lib/systemd/deb-systemd-helper-enabled/run-qemu.mount.dsh-also /var/lib/systemd/deb-systemd-helper-enabled/multi-user.target.wants/run-qemu.mount; systemctl status run-qemu.mount
ls: cannot access '/etc/systemd/system/multi-user.target.wants/run-qemu.mount': No such file or directory
-rw-r--r-- 1 root root  0 Jun 24 10:25 /var/lib/systemd/deb-systemd-helper-enabled/multi-user.target.wants/run-qemu.mount
-rw-r--r-- 1 root root 59 Jun 24 10:25 /var/lib/systemd/deb-systemd-helper-enabled/run-qemu.mount.dsh-also
○ run-qemu.mount - Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there
     Loaded: loaded (/lib/systemd/system/run-qemu.mount; disabled; vendor preset: enabled)
     Active: inactive (dead)
      Where: /run/qemu
       What: tmpfs

Jun 23 09:47:38 i-kvm systemd[1]: Mounting Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there...
Jun 23 09:47:38 i-kvm systemd[1]: Mounted Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there.
Jun 23 09:50:09 i-kvm systemd[1]: Unmounting /run/qemu...
Jun 23 09:50:09 i-kvm systemd[1]: run-qemu.mount: Deactivated successfully.
Jun 23 09:50:09 i-kvm systemd[1]: Unmounted /run/qemu.
Jun 24 09:40:31 i-kvm systemd[1]: Mounting Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there...
Jun 24 09:40:31 i-kvm systemd[1]: Mounted Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there.
Jun 24 09:45:36 i-kvm systemd[1]: Unmounting Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there...
Jun 24 09:45:36 i-kvm systemd[1]: run-qemu.mount: Deactivated successfully.
Jun 24 09:45:36 i-kvm systemd[1]: Unmounted Prepare /run/qemu to allow still running qemu binaries of former builds (after package upgrades) to fallback-load modules from there.