Weird X Problem

[Vaughn Treude]

Normally when I encounter a Linux problem my first course of action is 
to Google for a solution. This time I'm not even sure what to call it. 
"X Windows scroll problem" and "X Windows bad repaint" don't return any 
useful information.
I'm running Unbuntu Hardy Heron on a Dell Latitude D830.  So far the 
problem has only shown up when it's hooked to the docking station and 
connected to my Philips CM800 monitor.
Since the screens are different dimensions (4:3 and 16:9), it surprised 
me at first that it worked as well as it did. When I boot it with the 
monitor attached, it sets the resolution to match the Philips. On The 
Dell, the bottom of the screen is chopped off. That's OK for my purposes.
What's started happening is that window repainting has stopped working 
for certain actions. When I try to scroll a document in Open Office, the 
whole thing goes black. If I minimize and restore the window, it's OK. 
The problem also occurs when I drag a terminal window across the screen. 
That goes black as well. Again the problem can be fixed by minimize/restore.
The first time I encountered this, I figured that X Windows had gotten 
in a bad state, so I logged off and back on. (This has always been one 
of my favorite features of Linux; you don't have to reboot to fix a 
problem with the windowing system.) Now when I log off it never comes 
back to the log on screen; it just stays black. I end up rebooting it. 
The last couple of times I have done this, the problem is still there.
I've looked in the Xorg log file and all that's in there seems to relate 
to initialization of the monitors.
At some point I will probably get a new monitor (because of the 
dimensional issues) and give this one to my kid, but I've got no 
guarantee it won't also happen with the new monitor.
Has anyone else encountered this problem? Does it have a name?
Thanks in advance,

Vaughn