Two different ISBN's for two different books add the same one book using identifier import
Why are two different ISBN's importing the record for only the first of these two books:
9780061855887 - Volume 1
9780061855894 - Volume 2
9780061855887 - Volume 1
9780061855894 - Volume 2
http://lx2.loc.gov:210/LCDB?operation=searchRetrieve&version=1.1&query=bath.ISBN=^9780061855887&maximumRecords=1
http://lx2.loc.gov:210/LCDB?operation=searchRetrieve&version=1.1&query=bath.ISBN=^9780061855894&maximumRecords=1