During package installation, an empty file /cxref.XXXXXXXXXX is created by mktemp call in postinst. Later in the same postinst script, the basename of the file is used to create a temporary file in /tmp/. Neither of them are removed at the end of postinst, however the file in /tmp/ is removed on reboot by system-tmpfiles. I suggest to fix the mktemp call in line 8 of the postinst to CF=$(mktemp -p /tmp cxref.XXXXXXXX) and continue relying on systemd-tempfiles for cleaning up on next boot.