/usr/bin/aptitude-changelog-parser has:

eval {
    require Dpkg::Changelog::Parse;
    Dpkg::Changelog::Parse->import();
    1;
} or do {
    warn "warning: Dpkg::Changelog::Parse not present, install libdpkg-perl\n";
    exit 0;
};

But in case the second part is executed, aptitude displays nothing,
and the user has the impression that it is still waiting for data.
Changing the exit value to 1 makes aptitude display the old (cached?)
logs. See attached patch.

Note: there's still the issue that the warning disappears immediately
(this is similar to bug 1042897).