The problem still exists when in a classic GNOME session instead of Unity. It even exists when Compiz is disabled. So the 'i915' module seems to be faulty. Could someone please verify, whether this bug appears on notebooks from other vendors (not Lenovo systems) or even desktop systems as well, when the internal Intel HD Graphics is used? If so, we might file a bug report to the developers of the 'i915' module. If not, then it might be something specific to the hardware used within Lenovo systems and not a problem with the Intel HD Graphics.