Farmers don't share bread

If a farmer has 6 bread or 24 carrots, potatoes, beetroots, or 18 wheat in its inventory it should share some of this food with hungry villagers. I however can not get farmers who harvest wheat to share anything even though they build up a full inventory. Other farmers, such as those who harvest beetroots, potatoes and carrots are somewhat reluctant to share food as well and sometimes walk around with a full inventory too before sharing... but they do eventually share. Bread on the other hand I get none of.