If you are holding an item like a firework rocket, food item or empty map in your offhand (any item that has a right-click ability), then try to place a block right underneath you (or any surface that you are touching), you won't use your offhand item, even though your main hand item is unusable. Instead, although your offhand item is still very much usable, nothing at all will happen. This may be intended but it doesn't really make sense. Sorry if my wording doesn't make enough sense. Use the image attached to understand. I'm holding right-click in the attached image.