The property of soul sand that allows items to pass through it into a hopper isn't visually represented correctly when farmland, which looks shorter than soul sand, doesn't share this property.

What I expected to happen was the farmland block to allow items to pass through it to a hopper.

What actually happened was the items sat on top of the block.
This is because of the property of soul sand of having a height of .875 and the farmland having a height of 1, despite looking visually shorter than the soul sand.