See e.g. http://musicbrainz.org/edit/15627133. It enters barcode "0077779183524", but this barcode is already there (entered in http://musicbrainz.org/edit/14409277). Such edits just spam the edit queue...
MBServer should strip out barcode submissions from webservice, when they have same value as existing barcode
"Edit barcodes" edit should show the previous value