Heh, happens to me all the time!
Actually, what I usually find is that the second post (the "what he said" post) actually is the better and more detailed one because that person spent extra time making the answer better or more detailed. For example, you'll note that rlparker's post actually has a link to the control panel page where you actually add a sub-domain. That kind of stuff takes extra time to write up, but is well worth the effort from the perspective of the person asking the question!
It's of a very different character from the posts that are "let me post a shoddy answer quickly so my promo code can be the first reply". OTOH, I wouldn't want that kind of post to be confused with the "hmm, another post asking how to create a subdomain, rather than typing a long answer like I did last week, let me see if a short pointer to the right page is all it takes to help this guy".
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