I moved this question from Unix/Linux SE, since I think it fits here best.
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
but I cannot say for certain when the problem first occured.