Romanian here and not Polish, but Ukraine does hold (former Romanian) territory that it was handed to it by the Soviets, and some part of it by Stalin himself, Ukraine seems to have no qualms about that part of Russian rule.
A conversation can be had about Northern Bukovina, as the Habsburgs had stolen it first (in the 1770s) before it temporarily came back under Romanian rule in 1918, but the county of Herța[2] had been under Romanian rule ever since the first Romanian principalities were formed (in the late 1300s in the case of the Principality of Moldova). This latter piece of land was given directly to Ukraine by Stalin.
[1] https://en.wikipedia.org/wiki/Bukovina#Division_of_Bukovina