problem with user clip planes on GeForce 8800

Hallo everyone,
according to the OpenGL spec setting up a user clip plane is done wrt the model view matrix that is active at the time of setup. Hence, changes of the model view matrix AFTER the setup should not affect the clip planes. However, on my GeForce 8800GTX with driver 162.18 it does! Everything runs fine still with GeForce 7800GS even with driver 162.18 (and on all pre-8 series Nvidia hardware and all ATI hardware I tried). Did anyone experience this problem? Is there an explanation for this or is it simply a driver/hardware bug (to me it definitely looks like one)?