Is this a bug?

[Diadem]

This game is at normal game speed. I'm building Stonehenge, which is 120 hammers total, and I've done 73 hammers so far. Whipping gives 30 hammers per pop, so it should cost only 2 more pop to whip stonehenge.

But it costs me 4, according to the game.

What's going on here?

[Diadem]

As a result of this I failed to get stonehenge (my intuition was spot on. I just knew I would have to rush to get it).

As a charismatic leader, with 2 cities that are dying for a border expansion, loosing the race for stonehenge is not fun. Loosing it because of a weird bug is a reason to start over ...

[Nacht]

Wonders have double cost when hurrying (whether whipping or paying). It's defined by iHurryCostModifier in CIV4BuildingInfos.xml.

[Diadem]

Really?

Wow, I never knew. How is it possible I never noticed that before?

* Feels slightly silly *