Screen Edges

A strange thing happened. I opened libreoffice and plasma crashed. This is a regular occurrence since about 10 days that I had hoped would disappear with the arrival of kde-4.11.1, but it didn't. I closed libreoffice and tried to switch to another virtual desktop, when I noticed that screen edges no longer work. I just updated the system and a new kde-workspaces came, so I thought this just might be the fix, so I didn't worry about it. I restarted (not off and boot) the computer, expecting everything to be fine. It isn't. I checked systemsettings and the edges are set to active windows and desktop grid, but they are shown greyed out, so I thought that somehow these effects must have become disabled. They didn't. They are shown as enabled. I logged out and back in. Still the same. Ideas?