Near the back of the Catalyst logic board between the SCSI and monitor connections there is a VGA Enable jumper. If this jumper is closed, the onboard video is treated as the primary monitor even if there is no monitor attached to it. Consequently, any monitor attached to a video card will be either shifted severely to one side or will appear grey or will have the desktop pattern. Removing the VGA Enable jumper fixes the Issue.
Machines Affected: PowerCurve, PowerCenter, PowerTower