It seems when there are two policies active that give happiness from garrisoned units, only one is in effect. I have this in my current game.
I don't know if it is a bug , my scout has seen a natural wonder from 3 squares away I guess , and I got the bonus due to first explorer. BUT there was another Indian Archer just next to the wonder , they must have seen it before me...
So, it might be a bug.
<Row Tag="TXT_KEY_CIV5_FEATURES_NATURALWONDER_TEXT">
<Text>Natural Wonders are the great and glorious creations of nature that awe and inspire us all. The Grand Canyon of North America, Ayers Rock in Australia, Victoria Falls in Africa - all places that truly display the grand beauty of the natural world. In addition to providing wealth, [B]Natural Wonders trigger golden ages when first seen by a civilization[/B].</Text>
</Row>