There is no mention of radeon whatsoever in the dmesg (?) The first run boots with vesafb, as expected. The second one without. Since AFAIK, xf86-video-ati no longer knows how to do UMS, you're probably using xf86-video-fbdev in the first boot, and xf86-video-vesa in the second. No idea why it crashes in the first case though. Could you please attach Xorg logs for both cases? I'm curious. Please note that this may well be a separate bug from the Matrox case.