I changed the systemwide ambiance theme a bit (specifically the scrollbar css), and this works fine in gtk apps, but in kde apps nothing has changed. They still have the vanilla ambiance look. I tried rebooting too.
Btw I've disabled overlay scrollbars.
I looked at this question: Why don't Qt4 apps in Lubuntu pick up the GTK theme? and tried setting the Gtk+ theme in qtconfig but that didn't help. The look remains the same. Changing the theme in qtconfig to another one, such as QtCurve, does have an effect though.