This must be an ongoing issue. I had this problem with my old 660 and now with my 890. I emailed logitech. And told them the problem, And asked if i could pay to have it repaired. we emailed back and forth a few times. And now logitech is sending me a new 890.

On my 890 i remapped the volume up button the the mute button as a temporary fix. (i told them that too)
Just a heads up though. If they do set you up to receive a new remote they will deactivate your current one from being updated. So if you plan to do that temp fix do it first before you call/email.

now my only problem is. the 890's are on back order for 3 weeks.

Hope this helps.