I have a vague, undeveloped theory that the unconscious imposition of Western European understandings of "nationality" upon Eastern European reality was at the root of some of the contradictions and murkiness in Soviet nationalities policy.
[WS:] I think it is a bit more complicated than that. Nationalism was for a large part a 19th century reaction to the imperial domination of ethnically diverse EE by the Russian and Austro-Hungarian empires. In Poland, an additional impetus came from the quasi-colonial class structure. The downwardly mobile lesser gentry (the "szlachta") were pushed from the land by large scale land owners (the "magnates") aligned with the Russian empire, where they had to compete with non-Polish bourgeoisie (mainly Jewish and German). That explains the rabidly nationalistic and anti-Semitic sentiments of the segments of Polish intelligentsia. By contrast, the Czech intelligentsia developed from the urban classes and was far more progressive than its Polish counterparts.
Another element is that in contrast to Western Europe, the EE population was predominantly rural and shaped by feudal relations (a point also stressed by Brenner it is theory of capitalist development) - which meant basically two things: large masses of illiterate peasantry having little exposure to the outside world viewing with suspicion any sign of foreign influence. I think this peasant populism was at root of the Soviet nationalism, to which you refer.
Finally, there is the reactionary influence of organized religion. In Russia, there was little separation of the orthodox church and the tsarist state. In countries like Poland, which did not have their own state, religion was a substitute for state. As a result, nationalism was heavily sanctioned by religion.
Wojtek