For all these countries that the Red Army entered (Poland, Romania, part of Germany, Czechoslovakia, Hungary), the procedure was straightforward. Once the Soviets beat the Germans they become de facto occupants and could establish a government of their choice.
With Bulgaria it was a little bit different. Once it became clear that the Red Army offensive would enter their country, local communists swiftly executed a coup d'etat, which was obviously not opposed by either the Bulgarian public or the USSR. Even so, they still went under Soviet control.
In Yugoslavia, they had their own socialist government. However, since 1948 Yugoslavia was independent from USSR. As much as it is questionable if they were a part of the Eastern Bloc, they surely weren't under USSR power like the rest. (Albania had some similarities, also being independent since 1961. Albania was geographically separated from the Eastern Bloc in that it only bordered Yugoslavia.)
Somehow, it never occurred to me that the Red Army did enter Yugoslavia, and did take a major part in liberating the capital in 1944. What were the reasons for completely withdrawing their troops, and when did it happen? It is so unlike Stalin to do something like this. He could leave at least a few rear units and try to influence, if not control, the situation later. This would repeat the usual scenario that had played out previously. The West could object, but surely they wouldn't bring their own troops to Yugoslavia to escalate conflict, especially since everyone was still facing the Germans. It seems that it is somewhat exceptional that Yugoslavia was handled this way with respect to all the other countries where the Red Army "dropped by".