Solution
Matrox has released a firmware update for the RTMac card that addresses this issue. You can download it from:
Matrox RTMac software updates
http://www.matrox.com/video/support/rtmac/software/downloads/software.cfm
Note: Information about products not manufactured by Apple is provided for information purposes only, and does not constitute Apple's recommendation or endorsement. Please contact the vendor for additional information.