kpackagekit cannot display changelogs

Binary package hint: kpackagekit

I am using Kubuntu Jaunty with all updates. When there are new security or bug-fix updates available, I click the notify icon on the status bar, and kpackagekit shows up. Clicking on a specific package the following informations are displayed: type, new and old version, repository and changes. This last "changes" entry is always "The list of changes is not available". I can, however access the changelog by searching manually on the launchpad website. Maybe the URL that kpackagekit tries to open is wrong?
This can be easily tested by downgrading a random package in jaunty-updates to the jaunty version, e.g. sudo apt-get install ntpdate/jaunty, and update back via kpackagekit.