Attacking and killing 0?

I have had this happen to me a few times and it is happening more often it is a bug or what? I attack an enemy city with a sizeable force. Often times I should have won but despite that it shows me looseing all my troops while the enemy looses absolutely nothing. I thought after the first couple of times maybe it is just not showing their losses. But they still have all those units there after. Now there is NO WAY that this is how some battles turn out after the recent changes. Is it?! Has this happend to anyone else at all or is it just me? What do you think it could be?

Yes i've had this sometimes

Quick or casual? Did the attack move actually happen? Did he reinforce maybe?
Give an example of your and his troops please including numbers.

2 choice
-Reinforce Week
-Your enemie has tons of marines (depens on enemie strat, marines can defend first maybe )

Why would either of those things cause this?