[This ticket has been merged into MC-262454 and therefore should be marked as a duplicate of it. The original contents are preserved below for clarity's sake.]

The bug

In both the current vanilla textures and Programmer Art, there is a ring of unused pixels in the texture used for the top face of the hopper. While this texture is a rim which is three pixels wide, the actual rim of the hopper is only two pixels wide, so the innermost ring of pixels in the texture ends up going completely unused.

They appear to have first come into existence in the development of release 1.8 in 2014, when hoppers were first given proper, non-hardcoded models, but have remained unused.

How to fix

In both Programmer Art and the current default textures, these innermost pixels should be removed. I have fixed versions of both textures attached to this ticket.