window contents get partly destroyed when scrolling in KDE

[Wolfgang Jeltsch]

I use Kubuntu 9.04 beta on an AMD64. The line for my video hardware in the lspci output is the following:

01:05.0 VGA compatible controller: ATI Technologies Inc Radeon XPRESS 200M 5955 (PCIE)

I use the open source radeon driver.

Sometimes, when I scroll window contents with the scroll wheel of the mouse, parts of the window‘s content get overwritten with garbage, typically horizontal black and blue lines.

Please ask, if you need further info.