If you are having problems when in shaded mode whilst using Unigraphics V18, the following amendment to your systems registry should resolve the problem:
Run "regedit" and browse to the HKEY_CURRENT_USER/Software/Unigraphics Solutions/UG/180/Visualisation folder in your registry. In this folder there should be a string which looks like "(computer name) (computer name):0.0 GLINT R3 PT configuration". Find this then double click it to bring up the Edit String window. In the Value data box, change all instances of the word "display" and replace it with the word "immediate".