The Soviet "invasion of the eastern half of Poland" was nothing of the sort; not because they didn't invade but because to call the territory invaded "the eastern half of Poland" is just plain wrong. It was - at best - part Polish ethnically, much of it was 'really' Ukraine, Belarus, even parts of Lithuania. Most of it had been seized at gunpoint by the Polish military govt of the 1920s during illegal invasions carried out under the general heading of joining in the general western attempts to throttle the USSR at birth, but really a land-grab. The resulting territory usually ended up as great estates owned by Polish nobility with the locals reduced to an ethnically-based serfdom. Something of a model for the Nazi policy in the east a few years later in fact.
This explains the murderous Ukraine-Polish war that took place under Nazi occupation as Ukrainian nationalists resistance sought to ethnically cleanse Poles from the east and Polish resistance merrily reciprocated, for the most part leaving the Germans to get on with jew-slaughtering (which neither group seemed to greatly care about).
The current eastern borders of Poland basically mirror the Molotov-Ribbentrop line and no one apart from the lunatic fringes of the Polish far right seriously questions that they are about right in terms of where Poland 'really' is.