Package upgrade in Debian without corresponding changelog entry

[Ben Finney <ben+debian@benfinney.id.au>]

Howdy all,

Occasionally I notice a package upgrade on a host, but the Debian
changelog for the package has no corresponding changelog entry for the
new release.

The most recent example is ‘mercurial’:

=====
$ PACKAGE=mercurial

$ dpkg-query -W -f 'Version: ${Version}\n' $PACKAGE
Version: 1.4.1-1+b1

$ zcat /usr/share/doc/$PACKAGE/changelog.Debian.gz | dpkg-parsechangelog -l- | grep '^Version:'
Version: 1.4.1-1
=====

So, the version was upgraded to ‘1.2.1-1+b1’, but there latest entry in
the changelog is still only ‘1.4.1-1’. There is no entry describing the
changes in the latest release of the package, as specified in policy
§4.4.

How does this occur? A conversation on IRC suggested it might be related
to binNMU upgrades, but I don't know enough about that aspect to judge.

How can this be addressed so that changelog entries always accompany the
binary package for any new release of a package? Is this a bug in some
part of the system, and if so, where?

-- 
 \      “[I]t is impossible for anyone to begin to learn that which he |
  `\                thinks he already knows.” —Epictetus, _Discourses_ |
_o__)                                                                  |
Ben Finney