If your character possesses more than 6 titles, you will see a new scrolling side bar on the drop down menu in your Character pane (default: "C"). This change is to ensure that all titles belonging to your character will display within the drop down menu appropriately.
As a result, your drop down menu will be shortened, so it may appear as though some of your titles are missing. Please make sure to check for the scrolling side bar first, as your titles may simply be out of view. If the scrolling bar is not present and not all titles are displaying, it's best to proceed with a reset of your UI (http://us.blizzard.com/support/article.xml?locale=en_US&articleId=18761).