It may be a cable issue, but it's certainly not limited to the Scart connections. I have the same problem on a US Avant. No Scart connectors here.
I can sometimes hear my Tivo when listening to my AppleTV and visa versa.
If I unplug the Avant from the power outlet for a few minutes, the problem generally gets resolved.
I personally don't think it's a problem caused by cables, otherwise friends and family with NO B&O would also encounter this occasionally. It's just part of the charm of B&O. After all you have different "problems" caring for a thoroughbred than you do for a donkey.