Nouveau has a number of issues when a dual-link capable display is plugged into a single-link connector.
Affecting all boards: The detection of the display's native mode doesn't take into account whether a dual-link configuration is possible, so the driver will program the display with the dual-link resolution regardless.
On GeForce 8xxx and up: Detection of whether a connector is dual-link capable is broken, as is mode validation for dual-link modes.
Patches for all of the above issues have been available upstream for a while now.
Patch(es) available on kernel-2.6.32-52.el6
Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.