Font corruption in GTK2 apps

You can see what I mean here:
http://img500.imageshack.us/my.php?image=debianfontcorruption4vr.png

I'm running unstable.

It happens only in GTK2 apps (not GTK1, not Qt), with the notable
exception of Firefox (1.5), although I was under the impression that
one is also based on GTK2; however, neither pages nor menus/dialogs
are affected in Firefox.

I tried several DPI, same thing. The fonts are good, since I use the
almost exact same setup on another box (nearly identical xorg.conf and
font configuration), and no problem there.

I realise there are a LOT of things that could cause this: xorg,
fontconfig, xft, freetype, gtk or gnome libs... I'm just hoping
somebody has an idea of what I could do or test to narrow it down.

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