I'm sure somewhere, buried in the forum software settings is a "time out" setting that is improperly configured. This is exacerbated by the slow posting speed.
1. Person hits the "post" button
2. Software records the initiation of a post
3. Delay in posting
4. Software assumes post was successful and does not take into account the delay
5. Delay ends .. post is made.
6. Software sees this as an additional post made under the minimum repost setting.
7. Software shows the poster the minimum time between posts warning screen.
8. In the meantime the original post goes through as normal (although delayed).
Two problems here ... one is the delayed posting, two is the time-out configuration not adjusted to deal with it ... sometimes you get the time limit warning, other times both posts go through and a double post is made.
I think the crazy delay of posts is probably outside the limit of the variables that can be set for various time-out functions.
In a typical forum, these settings would most likely be available to the administrator of the forum and done "in-house". However the posting delay could very well the responsibility of whomever controls the servers on which the forum is housed. So it would basically require two people, both very familiar with their side of the system to coordinate to solve the problem.
Post delay = technical communication problem on the server side
Double post/warning = forum software configuration problem.
I suspect I am 100% Wrong. But it all seems plausible when I type it out
