Strange texture of Beacon blocks with a block on top of them

If you cover a beacon block, the top pixels of the obsidian base will change depending on the block covering it.
NOTE: The block must make the beacon deactivate! If the block doesn't shut off the beacon it won't work!
Screenshot 1: Normal beacon with no block on top of it.
Screenshot 2: The glitchy base after covering it with the Block of Emerald