So there definitely are differences in how the rules of engagement are interpreted from one actor to another. Needless to say this doesn't justify anything the Germans did and I acknowledge that Russia was instrumental in beating the - actual - Nazi's but still, that difference does stand out.
It's a pretty tricky thing because technically the Russians were 'on our side' and the Germans were clearly the enemy and just writing about it in an objective way is hard enough keeping in the back of your mind everything else that the Nazi's were up to.
+ Note that the Germans committed plenty of war crimes in Poland as well and that there were quite a few really bad things that happened in areas under German occupation, but on a relative scale they were considered the 'lesser of two evils' from the point of view of the civilian population that was not directly in the crosshairs of the Germans.