Setting KDE Task switcher to list windows from all screens

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http://unix.stackexchange.com – When I alt-tab in Kubuntu 12.04, the listed windows are from the current screen only. In the Task Switcher settings, the "List windows" option is set to "All desktops", a setting which I changed a couple of times just in case it gets fixed, but with no luck. It used to list all windows in the past. Since then: I changed the effect options (listed in Task Switcher) a month or two ago I applied several updates (system-wide, as in apt-get update/dist-upgrade ) but I cannot say for certain when the problem first occured. Any suggestions? (HowTos)