Comment 14 for bug 112238

This is an upstream issue. Here is the URL to their bug report: https://bugs.freedesktop.org/show_bug.cgi?id=11057

As I mentioned to them I compiled the driver that worked from a previous release and dropped it into the /usr/lib/xorg/modules/drivers directory, but the issue remained. This would tell me something in the X server itself has broken the MGA driver. You are right it is most likely something to do with the pixel clock of 150.00 MHz. I came to the same conclusion.