I would say this is normal based on my experience with my 2011 D at 18K miles.
What I have seen is that when regen starts, if it doesn't complete its cycle, the fan will stay on when turned off and the next time you start the car it will attempt to complete the previously interrupted regen cycle.
I confirmed this by the "heat smell" I always get during regen while stopped at a light with the window down. (And the poor mpg)
-Ed