Basically, I see it cause a lot of confusion that traded wolves aren't in any den, but aren't released, either. People almost always think it's a bug. I think it'd help if a very simple change could be made to basically label them in some way as "Currently being traded" or "Currently in Transit". That way, it wouldn't look like they just fell into the void! So it should suffice to clear up all the confusion surrounding the whole thing.