Knife from the middle of no where

Guys,

I bought BF4 and started playing since 10 days back, I mean what the is the problem of the knife it keeps slashing while firing.

I am not pressing the R3 button, I am sure 10000%

My controller is pretty fine in other games, despite that I paid for a brand new orignal controller for my PS3 for it but man this problem is killing the whole fun of this game.

Is it a issue with BF4 or is it a lag from my internet? please someone answer, other wise I will sell this game again regreting that I bought in the first place