As you see in the video, the villager won't pick up more than four stacks of seeds. I noticed it when i wanted to build a wheat farm. In the video the villager doesn't have a profession but i tried it with a farmer (level one to five), as well.
When i let the villager harvest, he was able to pick up additional wheat and had four stacks of seeds *plus *the wheat. So it only seems to affect items that the player gives him.
This occurred at every ingame-time and in multiple biomes. The villager had bed and workstation reachable that where also shown as his POI.