Very Odd. I have the exact same receivers. I use a Cinema7 in the main theater room and code 621 turns off the SAT-A4 reliably. I use another Cinema7 in the bedroom with the code 621 to turn off the SAT-A3 reliably. It may just be some subtle difference in you model/date. I know sony removed (left out) the discretes from the newer A50 receiver. It could be that they actually started on late model A4s.

BTW, in both Cinemas I use the device code 0639 for Sony SAT receivers.

On a whim, try the code 109 for discrete OFF. It's the "reduced" form of code 621.

Good luck,

Dave