While not game-breaking, it is for me game-ruining. Every enemy, at any distance and with any weapon, has a 95% head shot chance now. I'm certain this is not how that perk was intended to work. I do not have the Sniper perk or any other that increases head shot accuracy, and my PER is 7. What convinces me that it's a bug is that distance has no effect.

I have never used any cheats or exploits.

Same issue here for me. Hope there will be a fix to that soon.