Version:            (using KDE 4.3.1)
OS:                Linux
Installed from:    Ubuntu Packages

* Bug Description *
When a plasma notification or pop-up (such as when hovering the mouse over taskbar entries) appears, it will sometimes create a "hole" in a window elsewhere on the screen.  The "hole" appears as a section the size of the notification/pop-up cut out of a window (in other words, you can see the wallpaper through it).  The hole will remain there until something causes it to redraw that section of the screen.  It's kind-of hard to explain the appearance of this bug, so in lieu of a thousand words, please see the screenshot.

* Reproduction *
I have yet to be able to reproduce this with any kind of consistency; it seems to happen rather randomly.  The only thing I know for sure is that it does not happen with desktop effects enabled.

* Other Notes *
The screenshot has been manufactured, since I have been unable to capture this phenomenon in action.

* My System *
Motherboard: MSI K9N SLI Platinum (nForce 570 SLI chipset)
CPU: AMD Athlon(tm) 64 Processor 4000+
RAM: 2GB DDR2
Video: Dell NVIDIA GeForce 7800 GTX w/ 256 MB RAM (PCI Express)
OS: Kubuntu 9.04 i386 (with KDE 4.3.1)
Linux Kernel: 2.6.30-020630-generic
NVIDIA driver: 185.18.14
X.org: 7.4

* My custom xorg.conf settings *
    Option         "RenderAccel" "true"
    Option         "TwinView" "false"
    Option         "AddARGBGLXVisuals" "true"
    Option         "DynamicTwinView" "false"
    Option         "UseEvents" "false"
    Option         "TripleBuffer" "1"
    Option         "DamageEvents" "1"
    Option         "BackingStore" "1"
    Option         "PixmapCacheSize" "70000"
    Option         "OnDemandVBlankInterrupts" "true"