And actually some more. In the original Molotov-Ribbentrop plan, Lithuania belonged to Germany's influence sphere, but that was amended to become Soviet. And when Stalin grabbed Bessarabia from Romania, he also grabbed the Northern Bukovina which was not planned. Hitler did not protest, but then Romania was particularly the whipping boy among his allies - losing about one third of its territory.
Cough cough. Hitler also stuck to the bargain of Munich - for half a year.
True, Stalin should have known better, but I think he genuinely didn't believe that Hitler would risk a war on two fronts.