I hit a key by mistake and dunno what it was, not the draw distance in the preview window (both realtime and preview) is VERY short, and wont pick up lights/brushes etc if they are to far away...
ctrl + [ to increase sightdistance, ctrl + ] to decrease.
And the toggle button for wether you want to be using this option (cubic clipping) or not is located 2 spots to the right of the XYZ toggle button.