I set the background image for the treeview, but it changes the grey boundary area rather than the inside of the treeview itself.
(ie. the treeview stays w/ an annoying white background, but the edge changes colours)

Not a bug, i can't say really why but i think it's because the treeview is "drawn" in what you select for background so the treeview is drawn over

It's not a bug, but I agree that it looks bad. I would also prefer to be able to insert an image in the entire treebar. Of course, I don't use the treebar for that reason and others. Still, I'd like to be able to customize the format.