A post of mine from last year:
***
ObWI: Stalin gets *more* favorable boundaries with Poland in 1945. See Khrushchev's speech to the Ukrainian Supreme Soviet in March 1944 (greeted, needless to say, with "stormy applause"): "The Ukrainian people will seek to include in the Ukrainian Soviet state such primordial Ukrainian lands as the Kholm [Chelm] region, Hrubeshiv [Hrubieszow], Zamostia [Zamosc], Tomashiv [Tomaszow] [and] Iaroslav [Jaroslav]." S. M. Plokhy, *Yalta: The Price of Peace*, p. 185.
http://books.google.com/books?id=0wOKfjnXdAUC&pg=PT185
Khrushchev had a personal connection here--his wife Nina was a Ukrainian from the Chelm region--but it is hard to see him making claims like this without Stalin's prior approval. The Soviet Ukrainian historian Petrovsky (who was later to be accused of "bourgeois nationalism") quickly produced an article in *Radianska Ukraina* "The Primoridal Ukrainian Lands" to justify the claims--Danylo of Halych had died and been buried in Kholm, Khmelnytsky had claimed the area, the 1897 Russian census showed a Ukrainian majority, etc.
http://books.google.com/books?id=IzSEEqjp9vUC&pg=PA48
This was probably just a bargaining ploy, by which the USSR would "generously" concede these areas to Poland in return for the Western Allies (and of course Poland itself...) accepting the Curzon Line, including the loss of Lwow/Lvov/Lviv. But suppose Stalin had decided to follow through with the claim?