800x600 640x480 Modes ghosted on my twisterK

[Sérgio Monteiro Basto]

Hi! see if here I get some answer 

with driDevel enabled I got this problem on [ProSavage KN133](TwisterK)
5333:8d02 (rev 01)
first case:
with (default) Virtual 1024 768 on xorg.conf section display.

when switch to 800x600 (or 640x480) the image was correctly if virtual also
change to 800x600 (or 640x480) but has we know virtual stays in 1024x768 and
when I move viewport the image gets wrong (repeat left side).

second case:
with Virtual 800 600
Mode "800x600" also doesn't show image correctly but looks the same.

I think is just one problem of the resolution against virtual area of the screen.

where in source code can I find this calculations and init of Modes view ?

Can be  with dri only.
-- 
Sérgio M. B.