@aaaaa Makes sense now, but either way I never heard of it. Similar things happened in Yugoslavia, e.g. early on Albanians were referred to as Šiptars ( from Albanian Shqipetar) to make them feel more integrated, but it soon became a pejorative term among the people, so it was banned in the ’60s. There were many dos and don’ts during censuses.
@GLK There were negotiations between FPR Yugoslavia and Bulgaria, they started in 1944. Tito and Dimitrov were main figures in this, some agreements were signed in 1947. Stalin urged them to slow down because of situation in Greece, strong cooperation of YU and BG would be an excuse for western powers to increase military aid to Greece and Turkey. After 1948 it was logical why Soviets oppose it. Anyway Yugoslavia wanted Bulgaria to join already existing federation, Bulgaria wanted confederation.