Now I will be the first to admit that maybe I don't know how this feat works, however I have not been able to see the +1 ac in any situation. So I am thinking that this feat doesn't work. Here is what I have tried:
1. My character who has 20 ac with no weapon equipped, first equips a longsword (with the other hand empty), and later a short sword (with the other hand empty). In both cases the character screen shows no additional AC.
2. Thinking that the AC bonus might be hidden, I went to fight gremishkas since they are very accurate and hit low damage. After activating expertise (raising my AC to 25) I fought groups of Gremishka's, who were hitting me with roles like [17+8= 25]. This mean that there is no hidden AC, since the roll is equal to my displayed AC which was not changed by fighting one handed.
With no visible AC, and no hidden AC change, I can only assume that this feat is not working. Am I missing something?
Edit:
I was able to confirm that this feat only works with light and medium armor. I was using a piece of heavy armor.