It's not a bug. It's a natural consequence of the stupid "3 turns to build anything" rule.
If you rush an unit that should have been completed earlier, but wasn't because of the rule, you get paid for the wasted production.
Here is how I rationalize it.
[The auditor stomps on the construction site]
Auditor: Why hasn't the monument been erected yet? It's been half an year. We have more than 1200 citizens, and we should have been able to build it in one month!
Site manager: But, Sir, the construction estimate was nine months.
Auditor: Well, I can't get at the person responsible for that. But you'll be swinging from the gallows for pretending the building was not finished when it has been sitting idle for five months or so.
Auditor (to his squad): Take him to the executioner, and search his house for the wages and material costs he has been diverting from the project.
Auditor (to himself): Good thing I remembered to check, or two seasons would have been wasted. Now if I only could get at the people who pretend every project should take nearly an year.
