the current slowness of response has revealed (at least one of) the mechanism(s) of the noisome duplicate post. if while the Preview Post screen is up you happen to forget and click the Continue button multiple times you can get duplicate posts. this ordinarily takes exact timing, as there is a narrow window of opportunity before the software recognizes the entry and subsequently locks out further entries (you've all probably seen the message in this case). with the slow server response, this window is *much wider (and you are much more likely to forget that you've already continued). when response is normal, the anomaly is probably most often propagated by "mouse bounce" or the like.
-joe (unlocking another mysterium tremendum) friday