Comment 4 for bug 728434

This debhelper snippet in dbus.postinst is the problem:
# Automatically added by dh_installinit
if [ -e "/etc/init/dbus.conf" ]; then
        invoke-rc.d dbus start || exit $?
fi

In maverick (where this did not fail), it was:
# Automatically added by dh_installinit
if [ -e "/etc/init/dbus.conf" ]; then
        # start fails if already running
        start dbus || :
fi

Indeed, changing the dbus.postint to use 'start dbus || :' shows that dbus start fails, but the install continues:
$ apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up dbus (1.4.6-1ubuntu3) ...
start: Unknown job: dbus
invoke-rc.d: initscript dbus, action "start" failed.
$

The dash manpage shows that ':' is the equivalent to 'true'.