I guess that inspite of all the checks they do during assembly these days, now and then, something can still go wrong. I wouldn't over dramatize the situation. It's an overwhelming car you have there so don't let this triviality ruin the fun for you for the coming years...! I guess this car set you back sufficient euros so best try to enjoy it for its superior capabilities.
When you don't want the 535d anymore, I'am more than willing to exchange it for my 520d, it didn't have this weird phenomenon and it was entirely faultless until now (55tkms).