Debian packages can not go backwards in versions by design … If an Ubuntu package needs to be downgraded in the archive (due to some regression or some unfixable bug in the newer version), you have to play tricks with the version string.
Using “really${actual_version_inside}-0ubuntu0.x.y.z” is a pretty common scheme here …
(it gets really awful when a fix lands late and you do go forward again but without changing the major version, then you will have even more “really” or “actually” in the name )