When a farming villager has a full inventory, they will fixate on any dropped crops or seeds, stopping them from moving on to collect crops, plant seeds, or even hide at night.

Steps to reproduce:

Method 1:

1. Spawn a brown-coat villager and fill his inventory by dropping at least 8 stacks of seeds at his feet.
2. Build a simple farm nearby with fully grown wheat (bone meal).
3. Open the farm to the villager. He will collect the first plot, then stop after noticing the wheat item on the ground. He will not do any other tasks until the item is picked up by a player or despawns.

Method 2:

1. Locate a village in a freshly-made Creative world.
2. Throw several full stacks of seeds on the ground near the farmers.
3. Observe how as each farmer's inventory gets filled, they will eventually all stop and stare at the pile of seeds.