ive got a 06 d40 manual and just at every gear change i get a puff of black smoke, now you u can only tell ur misses "its because its a diesel" for so long...
fuel filter and reset ecu for starters. also check air filter.
odds are its probably just crap fuel.
also i would block or limit the egr especaily if your running on crap fuel.
and no its not because its a diesel. they should not smoke at all let alone enough for the driver to notice. "diesels should blow smoke" is just a PR line from fuel co's to sucker you in to using cheap crap fuel.
yeah i got k & n air filter so i dont know if thats causing a bit of a prob, yeah i was just getting the nags from the misses so told her something nice so she wouldnt go nuts and stress