Glitch with a sword, axe, shovel and pickaxe

Summary of the bug:

Expectation:
Regularly pressing the left button of a mouse four points of durability were taken away from my iron sword at murder of one zombie.

Reality:
It was taken away much more durability points.

How to recreate a glitch:
Two players. One in a survival, another in creative. The player in a survival hits the player in creativity by a sword. Durability of a sword was spent.