I would blink back the setup code for Audio using the 990 command, and see if it is still 31313.

A) still 31313 -- If vol and power both don't work, then re-assign 31313, and check again.

B) no longer 31313 -- Assign 31313 again, verify that vol works, press CBL/SAT, and see if that breaks it again. If it does, I would return it as defective. This fault is demonstratable in the store.

Basically, I would try to do a controlled experiment, demonstrating a repeatable seqeunce that breaks it. If it consistently breaks, the remote is defective.