If a hopper is locked with redstone, the items will still be sucked out of it if another hopper is below it. This is obviously a bug, sense if a hopper is locked, no items should come in or out of the hopper.
Related issues
Comments
Ezekiel
Duplicate of MC-6883.
same here. it wasn't happening before. this ruins many systems which are used for sorting and such.
I remember it being always like this.
This isn't a bug because the hopper isn't supposed to be able to control who interacts with it. The redstone prevents the hopper from performing actions, but does not prevent other hoppers from performing actions.