You are getting results that you didn't expect. In this case, uses is asked to enter a question. The user enters a questions and gets an error.
Maybe with your CSS changes it looks that simple. When you go through the flow you described earlier, you also have to title your thread, write a post, and choose a community for the post to go. It's all spelled out for you. If you just type iPad there the UI tells you that you can't post to "iPad," but that you can post to Using iPad and iPad in Business and Eduaction (check my post you replied to for a screenshot). If you don't put anything there, you can't post. If you try to select a community that doesn't exist or one you are not allowed to post to, it gives you an error and won't post. I can't see where the bug lies.
If you don't check off "I agree to the ToS" when signing up for an online account, and it doesn't let you sign up for said account, is that a bug or user error?