However, what is the sense of giving that information (assuming the statement of the YAK-40 crew is correct) to a the presidential aircraft of a foreign nation on a known official mission, if it is against the AIP?
There are different condition and rules for domestic or foreign planes in Russia. Despite the fact that TWR gave the clearance for 50m (I don’t believe it) the minimas of plane are still valid. Clearance to 50m is not against AIP, it only gives no sense for me. The responsibility stay in hands of PIC anyway. I dont think that ATCO was fully professional but it was PIC who continued descending below DH (or MDH).