In Gtk-2, a radio button set insensitive is "greyed out" - the label is grey, all the buttons are grey shaded and the surrounding space is grey. Backgrounds remain normal light grey.

In Gtk-3, the label is grey, but on a dark gray background (darker than the normal background grey), the buttons are not greyed at all, and the areas around the button rectangle are changed to a darker gray. A very strange looking effect.

Actually making the button insensitive works fine in both - only the visual is messed up.

An upstream problem, but I can't figure out bugzilla.gnome for the life of me. I have a 110 line test case (takes a lot to run GTK!).