I have a BenQ 1640 badged as a Plextor.
I always hold down the <Shift> key to prevent anything invasive from loading when I insert a disc.
Recently I did the same while listening to my Pretenders - Pirate Radio Box Set.
Disc 1 was recognized but 2, 3 and 4 were not recognized.
I had to load the last three discs without holding down the <Shift> key for the discs to be recognized.
BTW, every now and then, when this occurs, I can insert the disc into my Lite-On burner and it is recognized when I hold down the shift key.