Just make some tests with 2 different 2x4 +RW media both written on with the Benq 1640:
Fujifilm DVD+RW 2,4x RICOHJPNW01 --> BenQ 1640 doesn't recognized the media for reading! Toshiba 1612 reads it :doh:
Conmark DVD+RW 2,4x RITEK001 --> BenQ 1640 reads it, Toshiba 1612 doesn't recognized the media for reading :doh:
Both media written on with my old Sony DRU-510A can read both drives!