Noted this on both SB3 and Boom.

Browsed the bug database, but can't see anything similar. Filing under SC as SC seems to be the common component. Symptoms are:

Device is switched off (but still of course powered). Some random time later, with the device still apparently switched off, it starts playing via the line output. The display is blank. A Controller also shows nothing - just the default clock display

On the SB3, this has been noted twice - the device is connected to an amp which generally remains powered. On the second occasion, music started playing in the middle of the night - quite a shock! On the first occasion, it was reported to Logitech EU Support, log no 090917-000406.

On the Boom, this problem was noted today. The Boom is connected to a small powered subwoofer, which remains powered. The Line Out setting is set to Subwoofer. Bass tones were heard from the subwoofer; the Boom was still apparently switched off, with nothing showing on the display.

When the device is switched on, it shows the Now Playing info as the music playing when the device was switched off.

No alarms are set on either device. Both are connected wirelessly. I am not aware of any wireless network issues or interference. Running SC 7.3.3 as released, no additional plugins. SC is running on a dedicated PC server under WinXP Pro SP3. The server is permanently on and is connected to a wireless router using HomePlug devices.

I did start a forum thread about this: http://forums.slimdevices.com/showthread.php?t=67991
but not much response. Now it's happened on the Boom as well, I'm filing it here...