I think the Dublin agreement has been dead in the water for a number of years now. Fat Angie ran a coach and horses through it by unilaterally suspending it in 2015 and inviting one million Doctors, Scientists and Engineers to the fatherland. When she found out that not all of them were qualified in those subjects and that many were illiterate goat herders, that she tried to pass the latter on to other countries like the UK which to Camerons eternal credit- told her to do one.
Since then countries like Italy and Spain who are are the first to greet the new Europeans on their shores have complained that under Dublin they get lumbered with the problem and they should be shared by all EU countries. Brussels has agreed with this and stated that in the interest of EU solidarity refugees should be shared amongst all member states. The problem is that Viktor, he says "no" and his fellow bad boys (now the British have gone) have told Brussels 'they can stick that idea up their arrse.' Brussels has hummed and hawed and we are in a sort of limbo at the moment.
I read at the time that it was part of Frau Merkel´s cunning plan: she wanted to cherry-pick the educated refugees for German citizenship, and send the goatherders and camel drivers to the rest of the EU.
David Cameron did not tell Frau Merkel to ´Do One´, or at least he didn´t use those exact words, as although he didn´t want to be part of a quota system, he still accepted 1000 Syrian refugees in 2015, and agreed to accept another 20 000 over the next five years, but why let the truth get in the way of a good story.
Hungary effectively withdrew from the Dublin Convention, but I heard that very few immigrants wanted to live in Hungary anyway, as parts of it are just as backward as the countries they came from, there are few opportunities there, and the locals are rabid racists. Those refugees who were given asylum in Hungary left for another EU country as soon as they could get out.