The bug

You can place banners, brewing stands, singular glass panes, fence posts, turtle eggs, sea pickles, conduits, heads, iron bars, flower pots, signs, end rods, chains, and more items which visually do not fit on blocks with no visible top (such as composters, cauldrons, hoppers, and campfires.) Note: I would not be considering this a bug if every item that is like the ones I listed above could be placed on blocks with no visible top. Lanterns, torches, redstone components, and item frames.