When breaking the block with pressure plate on top (NOT the pressure plate) you will notice that the anvil, sand or gravel above it does not fall down. (See photo attached.)

A block update happens when you break either the pressure plate or the block beneath it. It is expected that the block above should fall in both situations. Here's an example: If I were to now place a block beneath with a torch on it, then break the block that the torch is on, the block above will fall instead of staying in mid air.