This is incredibly minor, but a bug nontheless.

I'm currently at my draft target, with draft set to reserve (49gc/soldier)
Last tick:
Draft Costs 15gc
Number of soldiers 0

If it matters, I also gained 1 peasant.
Obviously the game is charging a percentage, for a percentage of a sold (I was probably like .005 from the actual draft target or something)
So it's rounding the soldiers down, but not rounding the cost.