You won't have to use the ringer volume controls if you use the "Smart Ring Control" app:
Smart Ring Control
It does it automatically for you....
The local store says it's a warranty issue. I don't think so. I think it's a software glitch or a setting. Anyone else care to comment?
There is a new app on google play("Let It Ring") which is free and can control volume depending on your surrounding noise level with a lot of customization options. Install and enjoy using it, but please do not forget to comment/suggest improvements.