[StreamMan]

I think I have discovered a bug. I am unable to change the background of the menu item, "Favourites".

You should be able to set the background in the menu customizer, same as any other menu item. What happens when you try?

I created a menu item, "Favourites" with the action being the Common menu item, "Favourites"

Despite how I configure it, the background is always default_bg.jpg

I have had no problem setting backgrounds on all other menu items.