Aps on desktop disappear & reappear when mouse to bottom of screen KUbuntu 10.4 ; jor Xorg

[giovanni_re]

Didn't get an answer on KUbuntu list, so hopefully someone here might
have a suggestion.

==
I just switched from a vga to dvi monitor, & am now having this problem,
on KUbuntu 10.4.

When i move my mouse pointer down to the bottom of the screen, which is
supposed to pop up the task bar, all the applications on screen
disappear, & there is only a blank desktop with the task bar showing.

When I move my mouse pointer along the bottom of the screen, about every
quarter inch of screen movement the all the apps appear, then disappear,
again & again.

Anyone heard of anything like this?

I was using a sony vga monitor, & switched to a 5 yr old apple cinema
LCD DVI display, with a higher resolution.  I tested the monitor dual
head for several days, setting it to "clone" the display from the vga
monitor, & didn't see this happening.  When I removed the vga monitor,
this started happening.

Note: this is not me accidentally hitting the other "desktop" selectors.
 This will happen when the mouse is at the bottom middle of the screen,
nowhere near the other 'desktop' selector icons, which are at the left
bottom of the screen.

This looks like a bug somewhere, cause I doubt this could be a
"setting".  Where's the bug? KDE? X?

Thanks :)