[Marius]

The whole area around Warsaw was bombed on 10.9., not only the city itself. I don`t know anything about leaflets on this day.
In spite of the Bzura battle Luftwaffe was strong enough to carry out such a repression attack on Warsaw. For example also on 13.9. ca. 218 aircraft of Luftflotte 4 attacked military targets in Warsaw.

The order was never cancelled, because it was a draft only. As you will it never left the drawer. Such methods of attacks surely were discussed (as in every other nation`s high commands too). In Poland it was not needed to demoralize civilians, because Poland was too weak and the campaign took a fast end.

I think the reason for cancellation of the draft is going to an international matter. President Roosevelt send a note to the participating governments at the start of the war and everybody of them agreed (as I remember).
The other reason should be the fear of retaliatory attacks by French and RAF bombers.

I can "understand" that later RAF (divided from Germany by the English Channel) sought for any method to win the long war.
Maybe we will not find similar German orders for the period 1940-1941 as well, because Germany was repeatedly searching for peace with England. Such repression attacks against the enemy would make it impossible to gain peace.

Marius