Re: "clarified once the uncertain situation caused by Brexit has been resolved"
I ain't Spartacus,
Granted that the EU have not been exemplary in this, but we set the tone. If not May then the background yapping of Farage and the ERG with their rhetoric where we would just walk away from our commitments unless we got our way amongst other diplomatic and stately declarations.
It's a divorce, like it or not and emotion plays into it. Don't know what your experience in that department is but 9 times out of 10 it gets messy. From a negotiation point of view I can well see why the EU would not want us to dictate terms based on agreements they have with others, it sets a precedent for any others wanting to leave. Their goal is to keep the EU together and if that means making an example of us then so be it.
Expect to see the same tactic from BoJo if the Scots get pissed off enough to try to jump as well.
That is of course, if DC lets him.