A system crash at an inopportune time left my file system in a corrupted state. Fixing it up with fsck(1) worked just fine but made a subsequent system upgrade fail with an unusual error:
dpkg: error processing /var/cache/apt/archives/libfoo-1.2.3_amd64.deb (--unpack):
unable to install (supposed) new info file `/var/lib/dpkg/tmp.ci/symbols': Operation not permitted
The directory /var/lib/dpkg/tmp.ci
did not exist. Creating it manually and re-running
the upgrade failed exactly the same way (and removed the directory again.)