When posting a comment that is less than the minimum length, one can bypass the initial 'x to go...' validation by typing spaces, but clicking 'Add Comment' causes an orange error message to display stating that the comment isn't long enough (as a result of the server trimming the input and checking the length again). After receiving this 'too-short' error, if one corrects the length of the comment and tries clicking 'Add Comment' again they receive the rate-limiting 'You must wait 15 seconds to post another comment. Timer reset.' message.
The rate-limit error applied as a result of this bug applies to all questions, not just the one you are currently commenting on. The rate-limiting mechanism is incorrectly assuming that the submitted comment was successfully added even though server-side validation prevented it.