Could be caused by the settings (Admin->Posting->Default Editor) or by a Javascript error. You can check whether for example the categories and subcategories load correctly into the pull down menu when you are on the page to ask a question, and whether similar questions show up when you move from the "question in one sentence" to the "more information for your question".
I have experienced the same when the Facebook login plugin collided with the Share widget because of a FB library loaded twice. Disabling the Widget solved the problem (still can use sharing for single questions).
