Matrox G550 dual-head problem

[Mark Wilkinson]

I've just upgraded one of my systems from FC2 to FC3. One of the most
obvious problems I'm seeing is that the second head on my Matrox G550
doesn't get enabled when the X server is started by GDM. The server
*is* running in Xinerama mode though - the mouse pointer disappears
off the right hand side of the first head and comes back correctly.
The second monitor just sits there saying "No signal" though.

The workaround seems to be to flick back to one of the text consoles
(Ctrl-Alt-F1), then back to the X server (Alt-F7) - the second head
then springs to life.

Anyone else seeing this?

-Mark.