I use custome modelines particularly 720x540 on a TV, it was working fine since Ubuntu feisty, but when upgrading to gutsy, the display is now corrupted, the top half of the screen is kind of cloned on the half bottom part of the screen and there is a black separation that splitt the screen horizontally. The image doesn't seem interlaced by the way while it's what we want.
So I tried to put back the old xserver-xorg-video-ati driver and replaced 6.7.195 by 6.6.3 and then it works again.
So something went bad between this two modules.


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Section "Device"
	Identifier	"ATI Technologies Inc RV350 AP [Radeon 9600]"
	Driver		"radeon"
	BusID		"PCI:3:0:0"
	#VideoRam	262144
	#Option		"AGPMode" "4"
	Option		"ForceMinDotClock" "15MHz"
EndSection

Section "Monitor"
        Identifier   "TV"
        HorizSync    15.0 - 20.0
	VertRefresh  50.0 - 60.0	
        Option      "DPMS"
	Modeline "720x540" 15.101 720 778 850 968 540 561 566 624 +HSync +Vsync Interlace Composite

EndSection

#
#
##################################################################

I use ubuntu and upgraded for feisty to gutsy

the package for feisty are 
xserver-xorg-video-ati (1:6.6.3-2ubuntu6)
xserver-xorg-core (2:1.2.0-3ubuntu8)

and for gutsy
xserver-xorg-video-ati (1:6.7.195-1ubuntu2)
xserver-xorg-core (2:1.3.0.0.dfsg-12ubuntu8)