I'm playing Darius whose trait is 50% longer golden ages. 10 turns becomes 15. Pretty simple, huh? However something strange happens when you trigger a golden age (via policy or wonder) while already in one.

I had 9 turns left of a normal golden age (via happiness), and then I finished the Taj Mahal which triggers a golden age. I figure that it would just add 15 more turns to my existing golden age, for a total of 24 turns. Wrong! It now says 41 turns left. It gave me 32 more turns from building the Taj Mahal! Huh?

Anyone know how this works? Not that I'm complaining... but I wonder if it's a bug/exploit, because I can't figure out what math gave this result.