This appears to only happen on servers.
If attempt to hold down the mouse button in order to hit many tall grass/torch/etc. blocks that will break instantly, the punching animation will only show once and then will not occur, the blocks will still break.
1: Go on a server.
2: Find a patch of tall grass.
3: Look up at the sky and punch the air, still holding the mouse button.
4: While you're still holding down that mouse button, move your cross hair over the tall grass. It'll break, but the animation will not show.