I experienced the opposite, volume turning up rapidely (oh joy, late at night while neighbours sleep!) on its own.

I found it was somehow triggerred by widely opening a balcony door during winter while it was cold outside - as if it was IR controlled and stream of very cold air did it. I know it sounds incomprehensive but it happened exactly like that.

Would it be possible that you had as well some pattern of temperature change? Sorry I couldn't help better.

...and one more thing: perhaps this temperature "shock" didn't affect the Stage itself - but rather the Beoremote One and it sent signals "volume up" to Stage. That's another option.

AnalogPlanet wrote:

I found it was somehow triggerred by widely opening a balcony door during winter while it was cold outside - as if it was IR controlled and stream of very cold air did it.

I don't believe the Stage has IR capabilities.  I suspect that there's something going on with the touch sensors incorporated into the frame of the Stage.  Touch sensors can be a little tricky to design for reliable long-term operation across manufacturing and environmental variation.  I would expect B&O to have nailed it in their design, but perhaps the design team missed some use scenarios like sudden change of temperatures that could result in the behavior you've mentioned.