This appears to primarily stem from bad internet connections or large hang times related to high server load. I've implemented a 10 second flood control (i.e. you cannot post more frequently than once every 10 seconds). This should hopefully stop the system registering people hamming the 'Submit Reply' or 'Submit Thread' button too frequently.
Feel free to post here if you still see this problem occurring, but it should stop things like this happening (sorry to single you out, Tackle):