The live attenuated influenza vaccine (LAIV) currently licensed in Russia consists of the reassortant viruses with hemagglutinin (HA) and neuraminidase (NA) gene segments from the circulating wild-type viruses and the six internal protein-encoding gene segments from cold-adapted master donor viruses (MDV) A/Leningrad/134/17/57 (H2N2) or B/USSR/60/69. Presently, only classical reassortment technique is approved for the generation of Russian LAIV strains. In this work, we describe the obstacles to the development of LAIV 6:2 vaccine strains depending on the phenotypic properties of the wild-type viruses used for reassortment. It was demonstrated that the highest percentage of 6:2 vaccine reassortants could be achieved when wild-type parental viruses were resistant to non-specific gamma-inhibitors. It was shown that it was impossible to generate 6:2 vaccine reassortants possessing six internal genes of the AILeningrad113417/57 (H2N2) master donor virus and avian HA and NA genes from H5N1-PR8 viruses using classical reassortment technique. It was suggested that strong constellation effects between the gene segments of the parental viruses could affect the virus gene reassortment. A strong interaction between the genome segments encoding neuraminidase of avian origin and PB2 gene of PR8 virus was observed. When the PB2 gene was inherited from cold-adapted master donor virus, the neuraminidase was also found to be of MDV origin.