Are you referring to Poland? Well, Nazi plans to expand into the east were well known. As for the Soviets, a buffer with the Nazis was paramount. Not justifying their actions but looking from their perspective they were able to delay the war by two years. Even if the enemy was same, the objectives were vastly different. However, the enemy wasn't really the same considering Czechoslovakia, which the Soviets wanted to defend.
> Ended it with bilateral military parade. Supported each other with training and materiel right until summer 1941.
The parade was more or less just a show-off to fool each other. Just like how India-China have military drills(despite having territorial disputes) to soothe each other. Nazi-Soviets did have trade but from Soviets' perspective it was more likely done to avoid war.
When you say allies, what comes to my mind is US-UK or US-Israel relationship. Nazi-Soviet relationship was nothing close to that. I would agree with you if it we had been discussing this in 1938-41. But we have the benefit of hindsight.