Writing less than 15 characters in a comment triggers the 30 second protection.
Try to post a comment containing less than 15 non-space characters followed by the remaining number of spaces to make up the 15-character requirement. It'll come back saying the comment wasn't posted because it is shorter than 15 characters.
Then try to fix the comment and post it. It'll come back claiming you already posted a comment within the last 30 seconds, which is not true.