Since upgrading to KDE 4.11.1, i have experienced a simple annoying bug, and that is clicking an application window on the taskbar requires double click instead of single click. I never changed the KDE configuration, so i'm pretty sure it was a regression since 4.11.0. I reported this to Eric just before KDE 4.11.1 gets released, but he never had this issue on his machines, so i guess it's a problem on my own machines.
Later, i found out that my bug report is valid and it's really a regression, thanks to chrisretusn who found out a discussion on KDE Forum and that points to a bug report on KDE bug tracker. A patch has been issued and commited to the maste branch of KDE 4.11.x and it will be included in the next KDE 4.11.2.
Eric generously rebuild the kde-runtime package and include the patch into this build and upload it on his KTown repository. You should grab this package and upgrade your machines with this update. Log out from KDE and login again to have it fixed.
Finally i'm able to enjoy my KDE desktop again :)