Is Combat System Broken?

So I think combat system when attacking small stacks of 2 units is broken (this may extend to larger stacks but I am focusing on what I can test easily).

I have a stack of 5 Inf and 5 AC (Axis and all level 1 and slightly damaged 196.7 HP out of 200)

It is attacking a stack of 1 x Inf and 1 x AA (Axis and all level 1 and undamaged 34 out of 34 HP)

The combat is in a city

Stack info reports (and I know these are average and actual will be a bit different due to RNG

my stack will deal out 43.1 HP damage to the enemy

the enemy stack in defense will do 10.8 HP damage to me

So: my expectation is that I will have a pretty good chance of an immediate kill on this 2 stack

But no, the result is I kill the AA and leave the Inf completely undamaged and I take 7.4 HP damage

What I do not understand is why the Inf is completely undamaged at the end of the first combat round - I think the combat system is broken in this situation - I have seen this multiple times that is why I am reporting it here now