There are a couple of Iknow documents relating to your prblem, this may be the result of a partialy clogged DOC there is a special tool to clean it while staying on the bus. Check out Iknow document IK0700023 and IK1200478. Hope this helps!
Yes its common . I dont think there is a fix as its fuel washing down the cyllinders from the regeneration process. Id say just keep changing the oil often and dont ever let it idle.