No, I think it can remain functioning. It was previously being drawn with half transparency if the tree element was disabled (I don't know how to trigger this) or TE_DRAGGING flag was set (although this is never set anywhere anyway)

I wouldn't mind taking a look at this. I have pretty much the right behaviour as far as interactions by just replacing the icon with a button, but I guess the selection colouring/disabling are the trickier bits that aren't there yet.