Display errors with UGS NX

Hello,
I have the following question: using UGS NX with the free mesa drivers, 
curved shapes or surfaces with curved boundaries get rendered only 
partially, while flat surfaces get rendered correctly. This can be seen 
here: http://nas.dyndns.org/temp/Screenshot.png , and more obviously 
with more complex geometries here: 
http://nas.dyndns.org/temp/Screenshot-1.png . As far as I can remember, 
this issue was always present, first time I tested was mesa 7.6, and I 
tested with both intel and ati drivers.
While I am aware that this is a proprietary program and I would not be 
surprised if it was their code that is incorrect and only because of 
some miracle renders correctly on the proprietary nvidia/ati drivers, I 
still wonder whether this may not be a more trivial bug in the mesa drivers.
Thanks.
Regards,
Sandro Mani