Yeah, improving these dialogs is going to be on the soon-to-come voting list. I would like to eventually write a big custom canvas control that'll allow a real tree view with drag and drop (re)assignment of siblings and parents, but first of all the dialog could definitely do with some filtering just to make reviewing existing pairs better. Some of the workflow for rescinding pairs is borked as well.
I'll write a quick thing right now, though, to clip the text on that dialog!