Thanks for your update. Maybe I have to update the description first.

I think it's this change from 1.4.2:
"Fixed bug that caused subjects to cheekily draw manpower from their overlord instead of transferring manpower to the overlord."
I did some testing and they just changed manpower option from hardcoded prices file to add manpower instead of removing it. Sadly, it doesn't work with negative values

Hope they didnt change the way to handle those number, sure it still worked correctly in 1.4.1

Manpower gets added to the pool instead of being removed