Ahm, yeah, sorry. I forgot to mention that like remus I set them to use the oxygen-gtk theme (for both gtk2 and gtk3).
Other themes are working as expected. On Gtk2-apps the oxygen-gtk theme also works. (I tested this on gimp 2.8.6 which I believe uses gtk2; correct me if I'm wrong).

Okay, this is probably a bug in the Oxygen Gtk style then - I would suggest ensuring you have the latest version installed, and filing a bug report against Oxygen at bugs.kde.org so this can be investigated.

bcooksley wrote:Okay, this is probably a bug in the Oxygen Gtk style then - I would suggest ensuring you have the latest version installed, and filing a bug report against Oxygen at bugs.kde.org so this can be investigated.

I vaguely remember this issue being present on Kubuntu 12.04.
From memory uninstalling the kde-gtk-config module altogether did the trick.

This might be worth a try considering your at a dead end and are now familiar with the corresponding config files.

pagoda wrote:I vaguely remember this issue being present on Kubuntu 12.04.
From memory uninstalling the kde-gtk-config module altogether did the trick.

Unfortunately that didn't work for me.

bcooksley wrote:Okay, this is probably a bug in the Oxygen Gtk style then - I would suggest ensuring you have the latest version installed, and filing a bug report against Oxygen at bugs.kde.org so this can be investigated.

done: https://bugs.kde.org/show_bug.cgi?id=324059