Migrated question's answers can be upvoted twice by the same user
I've recently had a question moved from stackoverflow to superuser and noticed that the upvotes I had given answers did not carry through to my superuser account, however they did carry through in terms of keeping track of total upvotes. (I am 99% sure, I'll leave some room for maybe I'm wrong :P)
For example, I upvoted answers in the stackoverflow question, and let's say each answer now has one upvote.
When it's migrated to superuser, I am able to upvote with my superuser account - leaving each question now with 2 upvotes.
Is this by design? any thoughts?