Strange artefacts around some objects in GTK application - is it the Intel driver to be blamed?

[Łukasz Maśko]

My laptop has an Intel 945GM graphics and it is working more-less correctly 
(I'm using kernel 3.5.7, Intel driver 2.20.12 and xserver 1.13.0). But some 
time ago I've noticed some strange artefacts around menus or hint boxes (the 
ones that appear after you stop a mouse pointer on a button, for instance). 
I've made a screenshot, so you can observe it yourself: 
http://yen.ipipan.waw.pl/~ed/gtk.jpg
It happens in applications which use GTK (here it is Iceweasel, but it's the 
same for instance in Chromium or Gimp). KDE applications are free of this 
error. 

In the same time, I've noticed nothing like this on my workstation, which 
has an NVidia graphics, when using both proprietary NVidia driver or 
standard nv driver. The machines have exactly the same packages installed - 
excluding drivers, which are completly different.

I wonder, who is to be blamed here:
- gtk itself (although no such effets observed on NVidia card).
- intel graphics driver.
- anything else.

I'm using PLD Linux Distribution, but I don't think it's important here.
-- 
Łukasz Maśko                                                            _o)
Lukasz.Masko(at)ipipan.waw.pl                                           /\\
Registered Linux User #61028                                           _\_V
Ubuntu: staroafrykańskie słowo oznaczające "Nie umiem zainstalować Debiana"