There are 2 problems:

• the system doesn't check before entering data in Database
• the database has no constraints to prevent duplicated data

See http://musicbrainz.org/recording/b91df705-c3f7-4233-8026-8cdcae1d01e4 : it the same ISRC FRZ619500001 appears 4 times.

• One is pre-NGS,
• 2 have been posted post-NGS through ws/1 (http://musicbrainz.org/edit/14476662 + http://musicbrainz.org/edit/14476656)
• the last one have been added manually be me as a test (http://musicbrainz.org/edit/14477037)