Blocks retain hit damage when holding down the attack button outside range and moving in

If you hold down attack (left click) before you break a block and then move in to hit it sometimes it retains it's hit value. This happens on a dedicated server, LAN server and a single player world

What I expected to happen was...:
Attack damage should not be retained on the block

What actually happened was...:
Attack damage is retained on the block which breaks game mechanics

Steps to Reproduce:
1. Hold down attack whilst not hitting a block
2. Slowly move into the block whilst holding down attack
3. You should see the damage staying retained on the block