I actually find this annoying too, I would like to see the automated harvest wheat task changed.
Problem is that if I don't automate the wheat, I have to remember to harvest it or people will starve (Defeats the purpose of automating making baked goods) if I automate gathering the wheat to say 3 pieces, it will harvest 3, put them in the mill, harvest 3 more and keep putting them in the mill, in the end I'll have 75+ flour bags littering the area, storage rooms and scattered all over, with more being made because wheat never stock piles.
Basically it seems the auto harvest wheat setting is the number of villagers to dedicate to making flour, since they will just keep harvesting and making flour. Maybe change wheat production or tweak it somehow to take flour into consideration, or set a flour auto production that will harvest wheat automatically to turn into flour (IE you need 20 flour, when your down to 19 will send someone to the wheat field, harvest and make flour out of it to bring it back up to 20)
Right now auto harvesting wheat just leads to infinite flour supplies.