This is rather odd, unless the ECU has been touched after the remap. I believe there's another member who had experienced the same problem as you (same car, same mapper), only to be told that the car must have had an ECU reflash but in his dealer's book, non of such activity was ever recorded! In my books, bad move for the vendor to even suggest that!
My 335D is pulling stronger now I've put on another 2000 miles or so. Fuel economy is also going up with the engine loosening up. If anything, with time when the ECU adjusts, performance is optimized.
Definitely recommend a dyno check. I'm interested to find out more as if such has occured twice, something must be wrong.