When performing a heavy attack on an infected, it will often stun them so far back that a second hit will not reach them, I understand that this is probably intentional to give the player a chance to 'push back' infected when they are under attack by a group of infected but very rarely have I found a scenario when this would be spectacle given how it requires a lot of stamina and can therefore not be performed repeatedly whilst fighting a group of infected. In effect this far stun often means subsequent attacks miss the infected altogether and makes using heavy hits against them annoying, see video:

https://youtu.be/aP6TelNT5FU