# strace --output=/tmp/xx -ff dpkg -i /var/cache/apt/archives/grub-pc_2.06-2_amd64.deb shows plenty of which's still left, as you said. But apparently one is still not going to /dev/null for me.
Maybe you can send me a .deb with an set -x in /var/lib/dpkg/info/grub-pc.postinst so I don't have to repackage the whole package.
