Currently when an update to an already approved add-on is uploaded the review queue resets to the last position, there is no logical reason for this to happen.
The queue positions for add-on approval never reset when a new version is uploaded, the same behavior should extend to the update review queues as well.
Yes, I think that’s how it works right now - add-ons requesting review for the first time retain their position, updates on the other hand don’t. And this is a known bug, it’s merely that nobody fixed it yet.
That is correct, noitidart, as I said in the original post the queue doesn’t reset if the add-on has not yet been approved, only after it has been approved, every update you upload is reset to the end of the queue.
AMO development almost stopped a while ago, and it’s only picking up again now - so there are good chances that these ancient bugs will finally be fixed.