I think this is a regression compared to 4.8.0. If one has enabled icon tasks to show all tasks across desktops and activities and one clicks on a single task that is on another activity it changes to that activity. If however the task has multiple windows, e.g. kmail + the composer, this does not work anymore, i.e. clicking on the multiple tasks icon does nothing. If one clicks on the thumbnail that opens besides the panel it works.
This also affects KDE4.8. The reason, I think, is that when clicked on the group the 'present windows' effect is used, and this is not owrknig across activities. The only solution, AFAIK, would be to use the 'popup menu' setting for gouped tasks on another activity.
Git commit b268a60fa772a70e0f6ab50a39609bcea5c2418b by Craig Drummond. Committed on 08/03/2012 at 17:21. Pushed by craig into branch 'KDE/4.8'. When one, or more, members of a task group are on another activity then dont't use the present windows effect, fallback to the popup menu instead. M +15 -2 applets/icontasks/taskgroupitem.cpp http://commits.kde.org/kdeplasma-addons/b268a60fa772a70e0f6ab50a39609bcea5c2418b
Git commit 11bd0c1506062dce7699c71ad37fd76d441d23aa by Craig Drummond. Committed on 08/03/2012 at 17:26. Pushed by craig into branch 'master'. When one, or more, members of a task group are on another activity then dont't use the present windows effect, fallback to the popup menu instead. M +15 -2 applets/icontasks/taskgroupitem.cpp http://commits.kde.org/kdeplasma-addons/11bd0c1506062dce7699c71ad37fd76d441d23aa