I am not certain of this but thinking back I recall that rudder effectiveness on the F27 was significantly affected by Flap positions beyond 16.5 which did disrupt airflow over the rudder. There was a very significant increase in VMCA at actual Flap settings above the certified position which I think was 16.5. This serves to confirm the reduction of rudder effectiveness at high Flap settings.
The F27 as I recall was quite controllable in a crosswind at touch down speed but there was a noticeable rudder deficiency during the ground roll in the region between 50 and 30 knots and this coupled with the pneumatic brakes with full rudder applied was a handfull.
Perhaps it was a desire to improve rudder effectiveness which led to this procedure but I do not recall it as an SOP.