I don't have a clear answer for you unfortunately, but what kind of document results in this behavior? An assembly, a sheet metal part, simple part? Does it have derived configurations? What happens when you add a configuration, will it add one or six new configs?
You have 5 instances of an assembly that is flexible in a higher level assembly that is also open. SolidWorks creates 'secret' configurations in these flexible subassemblies that you aren't supposed to see.
See SPR 591968