Canada Picture Postage Design Rejected

I receive an email today from the Canadian Bank Note Company telling me that my latest Picture Postage (personal stamp) design had been rejected, because it included the Canadian flag in the photo. The picture was taken in downtown Vancouver and the large flag is draped around a building.



I find it quite shocking that we cannot put our own flag on personal postage! Does anyone know if there are such restrictions on U.S. personal stamps, or other those of countries?