From russian "pprune" (forumavia.ru):
If the takeoff to be completed with flaps28 - they should be retracted with 2 steps: speed 300 km/h - set flaps15, after acceleration to 330 km/h - set flaps up.
According info leaks somebody in the cockpit told : "speed 300.... f*ck, flaps!!! "
That's why there is a version that one of pilots selected flaps from 28 to 0 inadvertently.