GTK-Wimp

I'm drawing boxes and layouts with the descriptions "buttondefault"
respective "buttonlabel" in a TreeView. When doing this when wimp, wimp
creates warnings about not being able to cast GtkTreeView to GtkButton.
This is supposed to work fine, and works with other theme engines.

I'm supposed to be able to work around this by supplying NULL for the
widget argument (according to an IRC chat with a GTK developer), but when
doing so, wimp crashes the whole application.