I've noticed that Gtk+-3.4 has certain problems drawing user elements correctly. I experience it in www-client/midori (the only GTk3 app I've got installed right now) where the address bar is sort of "collapsed"/"shrunk" (lacks padding arround the text) and icon buttons look strange, too. At first I thought this was my theme not working correctly but it also happens with the default-theme after a fresh install. Here is a screenshot http://imgur.com/cGXgG
What exact gtk+ version do you have installed? Does it show the same problem when running under gnome? Have you tried to downgrade to gtk+-3.2.x to confirm it's really a gtk+-3.4 regression?
I've just learned that there is >=gnome-themes-standard-3.4 which indeed fixes the problem. Sorry for the confusion.