I was going to move my army into fog of war and I could preview combat with an enemy army I could not actually see. It seems this shouldn't be allowed as I was getting information within fog of war that should be hidden to me.

I experienced the same issue. I saw an enemy army go into a FoW, I clicked on my unit and hovered my mouse over a tile where I thought the enemy should be and I was surprised to see the preview of a battle.