GDM puts a semi-persistent "X" in the middle of the screen.

[Adam Funk <a24061@yahoo.com>]

When I log out of xfce4, the gdm login box appears normally.  Not long
afterwards, an "X" (like the multiplication symbol rather than the
letter) appears right in the middle of the screen.  When I log back in,
it stays on the screen until I run kmail or knode, either of which
makes it disappear.

I looked through the gdm bugreport page but didn't see anything.  I
suspect another package could cause the problem but I have no idea
where else to look.  Has anyone else noticed this?

Background: I currently have the following packages installed, although
this problem has persisted through upgrades for several months.
   gdm            2.4.4.7-3
   kmail          3.3.0-3
   knode          3.2.2-2
   xfce4          4.0.5-1

Thanks,
Adam