There is no pre-agreed treaty in the EU not to disperse them, either.
All the Dublin agreement was about was registering the supposed refugees so that they couldn't reapply under another name somewhere else every time they were rejected somewhere (for not being refugees but economic migrants for example). Many politicans then claimed it was about keeping them in the first country they entered, but that was just a nice little lie to please their populace -- which is pretty standard for many states. Lying about the EU to make themselves look better that is. Unfortunately it could come back and bite them in the ass.