Bullet stun

Some time ago I finished the diamond knife and now I'm starting to finish the bat, and I realized that every first bullet I took stuns me. So I started a private game against bots to do some testing and it turns out that it's only when you have a melee weapon in hand and when you're facing forward. It makes the knife and bat almost unplayable and it's incomprehensible (Sorry if my English is not perfect)