They have several pairs of questions which are the same problem. Some examples:
Their latest pair today, https://stackoverflow.com/questions/15349366/lock-cgrect-to-its-current-coordinates-objective-c and lock CGRect to current position – Objective-c can't be closed the way they should be under the new dupe closure rules because neither one has an answer.
(I've raised a flag about them, so I assume that there's no evidence that they're the same person.)
This isn't the end of the world, but it's kind of a stupid situation: they're clearly working on the same problems, and they're asking questions a couple of hours apart using very similar wording. (The questions aren't even followups, which would be just fine; they're really reposts.) There should be no reason they can't benefit from the answers to each others' questions. If these pairs were posted by the same user, we would be swarming all over them; I don't see a salient difference created by two accounts.
Closing one of the pair for another reason while dropping a duplicate link in a comment is possible, but doesn't seem ideal. What's the right way to handle this? Do I need to flag every time I see it happening?