It wasn't uncommon to do odd things with internal borders to divide people up in odd ways: the borders between the Central Asian republics bear little resemblance to anything that really existed before the mid-1930s; they were just drawn up by the top brass in the USSR to abritrarily divide people up into different nationalities that never really existed: and in many ways still don't.
The problem with Central Asia was that there weren't any national identities in the region before the Soviets.
Actually all 5 Central Asian republics exist in the same or roughly similar borders since 1924-1925, although initially most of them were subdivisions within larger entities (Kazakh ASSR was part of the RSFSR, Tajik ASSR was part of the Uzbek SSR etc.). And these borders, unlike pre-revolutionary ones, reflect ethno-linguistic divisions pretty well. But, of course, if people in some area speak the same language, it doesn't yet make them a nation.
