At the moment villager based (aka fully automatic) wheat farms are broken.
This is because Villagers will stop planting when their Inventory is full. A full inventory is of course a necessity if wheat is not to be picked up by the villager so it can be collected.
While it might be wise to limit the amount of seeds of a single type a villager can pick up villagers should continue planting their seeds and harvesting even if they can not, at the moment, pick up the crop.
I also found that while villagers do not seem to accept more the 4 stacks of a single type of seeds from the player they will still pick up this type of seed while harvesting. This seems strange to me because it might result in filling up their inventories with seeds (the exact thing which I suppose the original limit to 4 stacks should have prevented). I could not yet test this but this might break bread or beetroot farms too.
This might not be a bug but it feels at least unnecessary and inconsistent if it is intended