I think you are right! Although the disks were on sale for about $1 apiece, I am very disappointed in this drive. I bought it specifically because it was DL even though DL disks weren't readily available (or affordable) at that time.
I called Benq Canada helpline, and he told me I had to change the firmware to G7V9. However the burner will not take the firmware. Benq says it is a bulk drive and not a retail drive, however it has always shown up in the device manager as DD DW 1620 - indicating a retail drive.
Nonetheless, it is a piece of junk for DL burning. Great burner for single layer, but I think I am leaning towards a new Pioneer.