Just one thought that crossed my mind, when I ordered my Beosound 5 I specified 9 metre cables, the USB lead came with a 4 metre cable and a powered extension lead, when fitting the units in thier final position I found that I really only needed 5 metres, so replaced the powered extension lead with a shorter 1.5m non-powered one.
This caused the red light on my Beosound 5 to start blinking, every day I would return from work to find the red light blinking and the Beomaster 5 on, despite having checked in the morning before I left that it was in standby.
As soon as I swapped the unpowered USB extension lead back to the original powered one it stopped, and I havent had the 'blinking' problem again since.
Have you extended the USB lead by using a non-powered version?
regards
Paul