When I was talking to the sales man a few weeks ago he was asking if i'd noticed the car doing its regeneration, which I had and he asked did I notice the white 'puff' of smoke out of the back when it was finished, which I hadn't. He said once the regen was complete the collected particles get 'blown out' as a white puff of smoke.
I've still never noticed anything (other than as above about condensation) so I can't confirm or deny but could it be something to do with that or is it all the time? Are you getting a good run to allow a full regeneration?
Either way I think I would be popping into the dealers just as peace of mind and to make sure they are aware should something go wrong.