The problem with the rv250 on host a-865 has been solved via a PC BIOS change. Apparently AGP Aperture Size of 32 isn't sufficient for the rv250, while it was for the Matrox 550. Upping it to 64 made the rv250 behave as expected. I temporarily returned the Matrox 550 to a-865 to confirm 64 is no help for the problem originally reported here.