When tabbing around in the relationship editor, I've noticed it automatically selects the first element for each autocomplete dropdown. That can save a bit of time, but also can be a bit confusing if you tab quickly and don't even notice it happened. I suspect that might also be an extra confusing issue for screen reader users if their software tabs around to move?

Current autocompletes only select the first result on tabbing if you have actively searched for something, which seems like a good compromise - for other cases, it's probably not a lot of effort to press "down" once before tabbing to select.