I had the same issue. no time for bug reporting right now, but want to add something to the solution/workaround:
- the pkill command you should need only one time, if you have a non responsive process running already.
Once it is killed you can each time start it just withplasma-discover --backends packagekit-backend - You can edit the starter in the startmenu accordingly by adding
plasma-discover --backends packagekit-backendas visible in screenshot (keep the %F in order for discover to handle downloaded .deb files and such, i guess) - This will also affect starters in the control bar or on the desktop.
like this you can forget about it - atl east until the next update
