So, here it goes:
When playing via the "Hotseat" option as axis I saw this:
My opponent bought a new russian corps and placed it near Stalingrad. I attacked this new corps (strength 12) with a HQ, 2 tanks, 2 airfleets and 2 corpses (all german) and was not able to even reduce his strength. All my troops had already experience but nevertheless lost strength. This seems really weird to me.....
Explanations ?