If you click on the Main Rules link from the F.A.Q. & Rules page, one of the rules is listed:
"- Do not double post. If you think of something else to say before anyone else has posted, use the edit button, or prepare to be banned."
For as long as I've been a member of the forum, there's been a feature where if you post again when you were the last poster in a thread, the forum merges the two posts together and has an "Update From New Post Merge" line showing where one post ended and the other began.
Did the post merger feature make that rule obsolete and the page just hasn't been updated, or is it still there because people found ways to bypass it?