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:
Open the attached world.
Flip the lever down to activate/disable the hopper.
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.
Wait several seconds, observing that the item floats in the expected way.
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.
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While doing some experiments I found something you missed.
It has nothing to do with ticking order.
Try signaling only the dispenser while the hopper is disabled, by moving the block with a button on top of the dispenser. You can still reproduce the issue.
It's actually a disagreement about the location of dropped items.
If you try to pick up items dropped on the ground, you'll notice you can't. But if you break the bee hive and stand on top of the hopper, you magically pick up the item on the ground. This means the server thinks the item is inside the bee hive (or the hopper), but the client thinks of something else.
An interesting thing happens when you try to push an empty space on the hopper with a piston.
Place a piston horizontally facing the bee hive, break the bee hive, then activate the piston. The item dropped on the floor somehow teleports onto the hopper, then gets pushed out again. After that you can pick it up as normal.
GoldenHelmet
I think that MCPE-58866, MCPE-60159, and MCPE-62215 are essentially duplicates of this report, because they describe honey bottles appearing next to or inside hoppers that cannot be picked up, just as Pho describes the comment above. All are experiencing the same mechanics of hoppers not collecting items dispensed into a solid block above them. MCPE-58866 reports the bottles not being able to be picked up, this report describes the bottles being magically picked up.
MCPE-62215 mentions a similar bug in the Java Edition that was recently fixed, MC-165695, so this is also now a parity issue.
GoldenHelmet
I have found with further testing that the observed behavior described in this report only occurs if:
The dispenser faces into the east or west side of the solid block over the hopper.
There is a block with the right size/shape hitbox under the dispenser (glass, slabs, and daylight detectors induce the glitch; trapdoors, carpet, scaffolding, and glass panes do not).
When either of these conditions is not met, the item will not appear to glitch out to the side, and its shadow will be seen under the hopper.
Note that the difference between MCPE-58866 and this report derives from whether the dispenser is aimed into the side of a solid block (this report), or into the top of a solid block (MCPE-58866).
GoldenHelmet
This is not the same issue as MCPE-46746. This report is about the visual glitch that occurs when you dispense items directly into a solid block that is above a disabled hopper. MCPE-46746 is about items ending up inside a solid block above a hopper when broken by a piston from a block next to the solid block. In both cases the ability of a hopper to suck items from the block space above it is part of the demonstration, but that is just what hoppers do by design.
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(Tested before reported - from 'Technical Bugs List' https://docs.google.com/document/d/1nziKYzCr4pBdCRj2gIMlfr9MVdWHd6HyafdiBHx9F0c/edit)
This issue happens in 1.15.0.53 also.
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1.16.0.61 also
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Fixed in 1.16.0.63!
GoldenHelmet
Confirming this is fixed in 1.16.1, albeit indirectly. Dispensers simply no longer eject items into solid blocks. The items immediately glitch out to the north or west instead of beginning inside the solid block.
Auldrick