Once in a while, some well-meaning user appends the string " [closed]" to a question title after receiving a good answer. This is, of course, confusing to people who, for example, visit the question later and don't see a "closed as reason by voters at time" box.
I can't think of any case where this would be a desired behavior, so I propose rejecting any title that ends in " [closed]" except for the ones generated by the system for actually-closed questions. A quick explanation under "Oops! Your question couldn't be submitted because:" should be enough to make this feature non-confusing.