Radeon 8500, Xfree 4.3, DVI output, corruption

[Alex Perry <alex.perry@ieee.org>]

Using a vanilla Testing basic install and xserver-xfree86 version 4.3.0-7
with a Radeon 8500 (ATI brand) card and a Dell 20" LCD flat panel monitor.
Both card connectors (DVI and VGA) are plugged into the monitor for this.
I'm just trying to get as far as having the server up, and an xterm visible.

I can pretty much make any change to the config file and the xserver behaves
exactly as requested, in terms of what functionality goes on which monitor,
but the displayed image has the pixels permuted from their true locations.
It looks like the kind of effect when the drawing algorithm and the CRTC
can't agree on how to map rows and columns of pixels into the RAM buffer.
Providing you don't mind looking for the pixels that make up a given
character (in the xterm window) in a dozen-odd places on the monitor,
the system as a whole is running normally and applications are happy.

    HorizSync   31.5 - 69.0
    VertRefresh 59 - 61
    DefaultDepth 24
        Modes       "1600x1200" "640x480"
I've tried reducing the Vsync, Hsync, resolution, number of outputs in use.
None have any effect (except that resolution changes the permutation).

I'm assuming I should bring down the current CVS and try building that?
Or, is this a known problem for which there is a workaround to try?
I've done some googling and haven't found anything relevant (yet).

PS ...
In contrast, ATI's proprietary driver version 3.7.6 is different.
The behavior is consistent with "fglrx" thinking there is no cable
plugged into the DVI connector.  No corruption on the VGA output,
so it's basically usable but I don't get to have a Xinerama layout.