Well, here's how I saw it. In mIRC, the MDI, the toolbar, the switchbar, and every type of window can be given a background wallpaper that completely fills its respective inner surface area. If the treebar didn't offer background image selection, then that would be a simple inconsistency and nothing more than a potential feature request. But fitting the pattern that exists everywhere else, background image selection is in fact clearly offered for the treebar area, both via the menu option you get for it when right-clicking inside the treebar area, and by "/background -b", which is explicitly documented as being for filling the treebar. That said, when instead of filling that area the image fills a tiny 4 pixel-wide divider adjacent to it, I get a very clear impression that the issue is in fact a bug -- one consisting of the source code's background() function mistakenly targeting the wrong GUI object. Another reason: it doesn't make sense that Khaled would have purposely decided against giving the treebar background image support, yet in favor of giving background image support to its 4 pixel-wide divider -- something inherently so narrow that it doesn't even let you make out what's in the selected image.
