This is probably related to the "can't add actors to multiple episodes" bug, but I thought I'd mention it anyway. When I try to add a person to a series via the TV series' credits page, an individual episode page, or the actor's individual TV credits, the task goes straight through to moderation without giving a "Thanks!" screen (I have more than 5,000 points). Movie credits don't have this problem.
Got almost the same problem but it involves only one actor page - Lisa Tucker, she appears in The Vampire Diaries season 2 episodes 19-12, but every time I try to add her the page don't save. On episodes 19 and 20 there is currently wrong Lisa Tucker credited and would like to credit the correct one.