Basically if the same user posts two times in a row, both posts will merge. Found a mod, don't know if it works or not though : http://www.phpbbhacks.com/download/2206
in theory this is a good idea (and i am sure has been suggested before) however, there are some circumstances where you are allowed to double post and thus i feel that this should not be installed (unless some exceptions can be made about when to not merge) personnally i don't feel that we have a big problem on this site with people double posting so, for the time being at least, i would be happy to continue with the current system of having us mods combine double posts when we see them despite my own personal feelings, thanks for the suggestion and perhaps others will see this matter differently