D'you here that? It's the sound of a hopelessly stubborn Sirius fangirl trying to come up with a good hypothesis.

Er. Oh yes, here it is: when Sirius went through the curtain, he was not only trapped in his canine form, he was also split into various bodies--cloned, if you will, except not--which were then thrown at random into various corners of the earth, even though the earth is round and therefore hasn't got any quarters. To return to his proper existence, he must collect all of his various selves together and...go find someone who can put him back together. Or something. Obviously, this is taking a very long time, but I do wish someone had the sense to tell Harry. Or the Minstry, for that matter, except they'll probably screw up everything, as usual.