Since I upgraded to Kubuntu 14.04, an image of Google Chrome keeps popping up if Chrome is running in the background. It's only an image and it is enough to move the mouse pointer over the active window for this image to disappear, except in some parts of the window that are not refreshed. If I click on Chrome in the task bar it does not minimize. If I minimize Google Chrome its image stays on other windows but not on the desktop background. The same happens with Chromium and with no other application. I tried upgrading Nvidia driver but it did not help.