And in any event, surely Stalin was *at least as* certain that he would retain control of Poland as of his zone of Germany. So if other countries want Poland to be compensated for its loss of territory to the USSR (though some think the Oder-western Neisse line is a little too far), why should Stalin pick a quarrel with them over this issue?
At the time of Potsdam the W.Allies needed,or wanted Stalin to support them in the East against Japan,so will not aspect the Allies to push to hard for Poland to be compensated, which means that there are two responsibility the issues is postpone or it is doped. Another thing is that Stalin can claim a superior moral ground,by arguing that the Germans will have to be expel for the territories that are to be transfer to Poland,argument that will gain weight with of time.
So they need Stalin,they can not for force him,and Stalin can claim moral high ground.