It seems that now in 6.1 when you create your category you have to pass in "question" as the 5th parameter to the addCategory call instead of adding a question flag later. If you then want to mark an answer you need to do
1MBMessageLocalServiceUtil.updateAnswer(answer.getMessageId(), true, false);
instead of adding an answer flag like before. At least this is what did the trick for me.
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