I don't know if I have read your problem correctly. However, we have two machines here running upgraded KDE and when we log out, something strange happens. If we select Shutdown by pressing that button, additional questions are asked and it is difficult to get the machines to power off.
However, if we press the tiny downward arrow at the bottom of the Shutdown button, the machines power off successfully. I wonder if this is the same feature that you describe. We don't find it a serious problem and use the downward arrow as a workaround.