When I searched for Lee Dong Gun, on the search results page his birthday is July, 25th and on his profile it's July, 26th (the correct one). I have noticed it before, but cannot remember who the actors were, sorry.
Also, when I go to "Actors -> Hub", there are never more than 10 names listed, even if there are more actors listed in MDL database born on that day. Again, cannot remember who was missing and when, but if that were to help you, I could dig some more and find out :) Or is that on purpose and I'm just being a nuisance?