Believe me, I looked everywhere for this and couldn't find a duplicate.

When you try to lock a hopper only using a redstone torch or a redstone block, it won't work. If you try straight redstone dust pointing to the hopper however, it does lock. This only works with straight redstone dust, if you try to lock a hopper any other way it won't lock. 

Looking at past videos and pictures, this is not an attended feature.

Steps to reproduce:

• Place 3 hoppers, one on top of the other.
• Power the middle hopper using any redstone source.
• Put an item in the top hopper. Notice how the item still goes through, even if the middle hopper is powered by a redstone source, except for straight redstone dust.

What should happen:

The top hopper should always lock, no matter what's powering it.