If you look at a block, and then back up to the point in which the highlighted outline of the block in no longer visible, as show in my image, and then you press and hold left click to start breaking the block, your hand will swing and then do nothing. This so far is expected behaviour.
With left click still held down, if you start walking towards the block, there will come a point where you start breaking the block. To the user that is breaking the block, everything looks fine, however to a bystander, they cannot see the block breaking at all.

Note: If you hold down left click for longer than the duration that it takes to break the target block, or that target block on your crosshair changes during this process, the block break effect appears naturally to other players.