Just typical illogical Russian thinking
Recently I flew SU in Business International and ST E+ at the same time. I was given lounge access I guess based on my J-ticket. I was issued a lounge pass into one of the dingy lounge in Terminal F. I wanted to move to the slightly newer lounge at Terminal D (Aeroflot owned lounge). However, I got into a dispute with the lounge dragon that admitted that it was an Aeroflot lounge, a Skyteam lounge BUT since my flight was departing from Terminal F, I was denied access! I could have stayed to argue, but knowing that I was in Russia, I bit my tongue and held back from continuing the discussion.
I do not know what is wrong with SU's ground service, but it is clear that they are still operating in the 80's mentality. In the air, service has improved dramatically, it is just hell and heaven.
Cheers!