Since the upgrade to KDE SC 4.11.1 it is no longer possible to get a list of the grouped windows by clicking on the item. One has to wait for the tool tip to display the grouped items to be able to select them. In version 4.11.0 a simple click on the grouped icon showed a pop-up list. For my workflow this is a regression as there is a delay for the tool tip to show of 1-2 seconds, while the pop-up list was immediate when clicking on the taskbar icon. Widgets are locked, but even when unlocking them the behavior doesn't change. My taskbar settings: show tooltip maximum 1 row grouping by program name only show tasks from the current activity Disabling the tooltip makes the task manger grouped windows unusable.
You can disable "Show tooltips" until your distro backports the patch or upgrades to 4.11.2. *** This bug has been marked as a duplicate of bug 324470 ***
(To explain: The problem here isn't that the popup is gone, but that due to a bug in Plasma's MouseEventListener QML component, activating a task item - and that includes showing the popup for a group parent item - requires a double-click instead of a single-click. Disabling tooltips avoids tripping this bug because it removes a mouse event handler - the one handling tooltip activation - from the item hierarchy. FWIW, I've mailed Riddell the recommendation to backport the kde-runtime fix that addresses this.)
And they fixed it already, thanks a bunch :)