Possibly it is, but probably not.
The only way I can see ending up with worlds in different spots like this would be from logging into Windows using different named accounts. The "My Documents\My Games\" folder is really "Username's Documents" and so it changes depending on the user
that is logged in.
However, if this were the case it would mean that when you load the Terraria server to load the map you'd only see the 5th map and not the first four created under the other account name.
There might be another explanation but this is the only one I can think of at the moment.