Description of problem:
The critical update popup can be invoked multiple times, filling up the screen.
It's a bit ugly ;-)

Version-Release number of selected component (if applicable):
seen in rawhide just before release, and now in F9 GA.
gnome-packagekit-0.1.12-12.20080430.fc9.i386
PackageKit-0.1.12-10.20080505.fc9.i386
PackageKit-libs-0.1.12-10.20080505.fc9.i386
yum-packagekit-0.1.12-10.20080505.fc9.i386

How reproducible: since it occurs autonomously not that easy. It depends on what
PK is doing {that you can't see}

Steps to Reproduce:
A:
1. click check updates from the PK applet icon after being notified that they exist.
2. unselect all
3. check a package of interest
4. apply an update that does not include the critical update

B:
1. F9, login to gnome session. 
2. {possibly there was already one noti before screen saver kicked in, but I
wasn't there to see if that was the case.}
3. wait until screen saver.
4. move mouse/hit key
5. type password.
  
Actual results:
A: 
After seeing a second copy if the notification, I repeated the process multiple
times to see if it could be reproduced - see the attachment.

B:
two critical warning dialogs are shown, one at the bottom, the other at top centre.

Expected results:
PK should keep track of it's bits. One ominous {yet totally irrelevant} warning
is quite enough.