Dear Brogaard and Szabo,
I think what you have experienced is something related to the lens and not the imaging element itself. The lenses that you used do not exist (50mm f/1.2 and 80mm f/1.2) but in case you used the 50mm f/1.0 and the 85mm f/1.2, yes they suffer from a small amount of distortion.
The distortion has been seen by others too, as can be assesed by checking http://www.photozone.de/bindex2.html .
One of the best lenses to get straight lines would probably be the 90mm L TS-E, or one of the 600mm lenses.
Regards,
Andre :p