Under the right circumstances, a hopper can suck an item entity that is beside and below it. The behavior is triggered by precise timing of a redstone signal applied to the hopper.

Screenshot and demo world are attached.

Steps to reproduce:

1. Open the attached world.
2. Flip the lever down to activate/disable the hopper.
3. Press the button on the quartz block. This activates the dispenser and hopper together, which seems to create the precise timing condition. The dispenser shoots an item into a solid block, and the block pushes it out the side where it falls to the ground.
4. Wait several seconds, observing that the item floats in the expected way.
5. Flip the lever up to deactivate/enable the hopper.

Expected result:
The item remains on the ground since it's not in a position where the hopper can suck it.

Actual results:
As soon as the hopper is enabled, the item disappears. Inspecting the chest shows that it was sucked by the hopper and then pushed into the chest.

Additional information:
Using the lever to disable the hopper is not necessary to cause the bugged behavior. If you don't use it, the item still drops to the ground but gets sucked by the hopper when the button deactivates instead. I added the lever to show that it doesn't matter how long the hopper remains disabled, it will still suck the item when it becomes enabled again.

I originally discovered this bug in the context of a honey farm. If you replace the planks with a beehive, you'll have the core of such a farm and its structure is something a lot of people would intuitively choose. So while this bug may seem esoteric, it isn't necessarily so.

Although I didn't have any trouble reproducing this bug, it could plausibly be dependent on redstone update order, which I couldn't control. If it doesn't behave as described above, you might have to break and replace various redstone components a few times to reproduce it.