Plasma taskbar corrupts in time with blinking cursor from thunderbird

[Vik]

Using KDE 4.2 on Ubuntu 8.10 on x86. Nvidia GeForce 7300 installed with closed-source driver - otherwise working well.

To cause corruption, open Thunderbird (2.0.0.19 used, but it seems version-agnostic), create a new mail message and click on the message content box as if you're going to write something. A flashing cursor will appear in said box as you would expect.

Now hover the mouse pointer over the Thunderbird tab on the taskbar. The tab will flicker and corrupt its colours, some taskbar entries may disappear. This will happen with other tabs and is not specific to having Thunderbird installed - it has also been observed with OpenOffice 3.0

Click back onto a static area such as Address Book entries, and repeat hovering the mouse pointer. No further corruption occurs.

Click on the desktop background, and the corruption disappears.

This problem will *not* occur with the flashing cursor in the Firefox browser's editing fields.