There's this answer on a Web Apps question migrated from Super User.
The poster has an account on Web Apps which is associated with his Super User account, but as you can see the answer hasn't been associated with his account.
Is there anything a moderator can do or is this something a dev has to do?
Given that it is something that a dev has to do (see Marc's comment) there's two further things that this highlights:
Do we need an easier way of flagging this sort of thing to the development team other than e-mail or raising a question on (a) Meta?
Why does there seem to be an increase in the number of questions and answers that don't get relinked to their owners after migration.
This question on Super User demonstrates the problem as well. The question's been migrated, the user has linked accounts, but the question isn't owned by anyone.