Comment 2 for bug 1063249

I am pretty sure the bug is hidden in unity/plugins/unityshell/src/UnityShowdesktopHandler.cpp, probably in

void ShowdesktopHandler::PaintOpacity (unsigned short &opacity)
{
  if (progress_ == 1.0f || progress_ == 0.0f)
    opacity = std::numeric_limits <unsigned short>::max();
  else
    opacity *= (1.0f - progress_);
}