When adding or removing workers from a project, the new production time is calculated incorrectly. Specifically, the game acts as if the workers had been assigned to that project from the very start, rather than just being assigned now.

For example, for one worker to create Shiva Rounds takes 100 hours. After 8 hours production the time remaining is 92 hours.
If one then assigns nine more workers to the project then it would be logical for the remaining time to be adjusted to 9.2 hours (i.e., ten times faster).
Instead, the game adjusts the time to 2 hours (i.e., 10 hours for 10 workers to complete the project, minus 8 hours already spent)!
If this calculation gives a negative number, the project will complete almost instantly.