Comment 13 for bug 546607

$ sudo apt-get upgrade
...
The following packages will be upgraded:
  libpackagekit-glib2-12 libpackagekit-qt-12 packagekit packagekit-backend-apt python-packagekit
...

I can confirm the bug is fixed in your packages. I added an invalid source and made sure the bug was still there before the upgrade, and it was. After the upgrade I no longer get any kind of error/warning after refreshing package cache from KPackageKit.

Maybe warnings/errors encountered during update should be shown as such, so the user knows something went wrong (missing repository, missing keys etc). Anyway, this would be the subject of another bug/feature report.