Just reporting something I found, not sure if it was on purpose or a bug, but when you stand on a hopper, you sometimes, and it is on every hopper block, fall into it, as if it was hollow.
MC-10027
Hopper Bug
Resolved
Works As Intended
0
Well, it is partially hollow, and your body is able to fit in the small hole it has in the center. This in intended, I believe. (Just like how you can jump into cauldrons)