Me too Jane...
I just sent a PM about it:
I have been experiencing the same problem and I am see the duplicate posts on other threads as well. When I post something nothing happens, then I get a message saying "allow 30 seconds between posts". So, I go look at the thread and nothing, no post. I figured it was some kind of glitch so I tried to post again, same thing happens. Eventually (about 5-10 minutes later) the post shows up. I actually ended up with 5 duplicate posts the first time it happened.
So, apparently the posts are hanging somewhere and taking a really long time to finally show up.
I think I will drop adnoid a note about it....
The key is patience, something I do not have alot of LOL.
ETA: If you need to delete duplicate messages:
First click on "edit" then click on "delete" then change the clickable button to "delete message" then click on "delete this message".