Evidently there is some sort of problem causing the server to be slow. When making replies or editing your post you may get an error or time -out message. Don't just go back & re-submit it again. If you will check the topic you will probably see that the post was in fact posted. Re- submitting simply posts it again & again, further slowing the server & adding to the problem
I discovered this accidentally & haven't had any problems with posting duplicates.