Their is a very interesting topic on the Multistrada.net forum. Its rather long and takes ages to read, but in short 6 members of the forum with 2003/4 bikes 5 of which have top box’s fitted (the other 1 does not say) have suffered a failure of the rear sub frame, which if you were carrying a pillion at the time could be somewhat tragic.
Also it wold appear that from sometime around 2004 Ducati carried out an unanounced mod to the subframe adding and extra brace, beefing up the whole structure.
Do we have any other info between us to add to this?