Mail 6.0 has duplicate "On My Mac" folder structures

Question

Having upgraded to ML 10.8 this morning I notice that Mail has two "On My Mac" folder structures below Archive, one is immediately below Archive (i.e. the top of the sub-tree) let's call it 1st instance, followed by iCloud, then the 2nd instance of an "On My Mac" folder structure.
From the erratic behaviour of the disclosure triangles in the 1st, this would appear to be the unwanted child. Click its triangle and the 2nd structure opens.
Now click the Archive disclosure triangle twice, once to close it all up, the 2nd click gives both "On My Mac" structures open to the first level, iCloud is unaffected. Repeat this operation and both "On My Mac" structures are closed up.
If you do open a sub-folder in the 1st instance, any subsequent click of the triangle is ignored, even in the other instance.
The 2nd instance is completely consistent in operation as would be expected under normal circumstances.
Closing and reopening Mail just remembers the current expanded state, the only consistent reset is achieved with the Archive close/open double manoeuvre.
Message was edited by: additall
Hmm, this was happening back in 2007, but the drag it out and back solution doesn't seem to work this time

Answer 1

Update, I think I've solved it for myself.
Previously, I had created a local folder called Archive. iCloud also comes with a default folder called Archive and Mail 6.0 was showing my local archive and combining it with its iCloud version, rather like the way that calendars and contacts get doubled up when your local stuff is mirrored on iCloud.
Having taken a backup of my local archive I trashed the lot, everything from the 2nd "On My Mac" tree downwards and then the other two sibling trees, the 1st "On My Mac" and "iCloud" just disappeared as well.
So my recommendation is don't use "Archive" as a local folder name.
I later created a test folder called "Local" and selected its location as "On My Mac". "On My Mac" is now listed in capitals, in a lighter grey colour, with the Hide/Show popup choice to its right. This is your local storage area, away from iCloud and Apple's little helpers :-)