I'm sorry, but I can only repeat and confirm that, every "double something" problem, is NEVER a problem of the scenery and it's ALWAYS caused by another AFCAD (or regular scenery) in conflict.
Yes, you have a duplicate AFCAD, fact you haven't found it or you haven't installed another scenery for the same airport, doesn't mean you don't have it. AFCADs doesn't necessarily come with other sceneries, the most common source of problems are those coming with AI Traffic packages like My Traffic, they must be manually removed.
Of course, this assuming you are keeping KDFW on the topmost level in the Scenery Library, which is where the installer puts it by default. If you moved, then anything might happen, and chances for double objects becomes more likely.