Confirmed... sort of
Just loaded up to a previous turn and retried. As the new turn messages began appearing (spell finished research), I happened to have the map centered on my city. Just behind the 'pick a new spell to research' window, I could make out an owned army standing next to my city consisting of Nephaz, the Sentinel (that had just been completed this turn), and the two freebie city archers. After I picked a spell, I then saw the 'you're being attacked!' message window.
Finally, after the successful battle--which was on the city map--I verified that Nephaz had been duplicated. He is both in the city and is in the army just outside the city (he was the only garrisoned unit prior to the battle).
Interestingly enough, when I click on Nephaz in the city and try to move him out, the whole army stack from outside the city moves to the same position, the screen shows there are two armies on that tile, but clicking on the arrows to scroll between the two armies does not select anything else except the army stack. I individually selected Nephaz and moved him out of the army stack, and now there are not duplicate Nephaz's.