background of KDE pannel is half-black when using 100% of screen width

The background of the pannel on the left side (K menu through running tasks) is
black while the right side is OK?

Although the screenshot is taken on a quad-head T-configuration in Xinerama
mode with Xorg it did also happened on a normal single display.

I tried Ubuntu's ppa packages to see if a newer version of KDE/QT would fix
that. The problem is still present with KDE 4.4.5 but disappears using KDE 4.5
(RC2).

Would be great if the patch applied to KDE 4.5 could be backported to KDE 4.4.x
or QT (depending of where it is...) or to simply upgrade to KDE 4.5

I'll post a screen shot to show the behaviour.