To the end user, there is very little difference. It's not doing what the user expects, regardless of intent or lack of intent on the part of the manufacturer.

I agree. The bug is bad enough - it would be an appalling QA failure. The design decision is much worse - maybe worthy of a class-action lawsuit.

So: Is it a bug, or is it a deliberate "feature"? Is there any evidence, one way or the other?

For people like me, that's an irrelevant detail. I don't even want to think about buying a TV that can't get volume control right. It's a basic feature that should never break - and one shouldn't have to wait for a firmware update.