I've been having problems with the forum's anti-spam filter that stops people from posting within 60 seconds.
I've played around with it, and it appears that when you attempt to post a message within 60 seconds of the last one, the message is registered, whether or not it actually went through. (Although it doesn't show up or effect post counts)
In other words, when I try to post, first it will say "You have posted a message in the last 60 seconds, please wait and try again." Then I wait the 60 seconds and try again and it says "You have already posted this message. Perhaps you hit the 'send' button twice."
Then, when I refresh and try again, it goes back to the "You have posted a message in the last 60 seconds, please wait and try again" message and I have to wait another 60 seconds.
The only way to overcome this seems to be if I stop trying to post, save my message and exit the thread, then completely try again 60 seconds later.