Rush granary, switch to courthouse for no additional cost

[Donny Brook]

Perhaps this is a well known bug, but I tried to search and could find nothing. I've rushed a granary (for X gold) and get a full production box of 60 shields. I then switch to courthouse. It tells me "do you know you'll waste X shields?" I say yes. It then gives a full production box of 80 shields for a complete courthouse. There is no additional cost for these extra 20 shields. In fact, it tells me I'm gonna waste shields by making the switch.

[Aabraxan]

Does this happen consistently? Do you have any shields in the box when you rush the granary?

[Donny Brook]

I stumbled across it by accident and have only played a couple turns since then, so I can't say whether it's happening consistently or not. Yes, I had part-built something (with the aid of civ engineers btw). The situation is that I'm in the milking phase of a histo HOF attempt (~ 1750AD). I was building something of marginal benefit (say a granary which would let me grow a couple turns faster). I cash rushed it, then decided a courthouse might be better. That's when I got the warning about wasted shields and the magical fully built courthouse. I could PM a game save to someone who looks into these things if needed.

[Donny Brook]

1. Go to Gewauga 2 and switch the build to Granary.
2. Cash rush the granary.
3. Change the build to courthouse. It will tell you "do you know you'll waste 10 shields?". Say yes.
4. The 80 shield production box for a courthouse is full, indicating it will complete on the next turn. There is no additional cost for these extra 20 shields.
5. End turn. The courthouse is complete at the start of the next turn.

[Mathias]

This is repeatable/exploitable. The accumulated CE shields are counted to reduce the cost of rushing the cheaper building, then also added to bin when switching to a more expensive building.