Well i doubt you have played any Europa Universalis game then! I have around 100 hours for every game and 300 for EU3 and i've encountered no bugs ;)
I'm not talking about actual bugs but rather flawed game play like hyper assimilation in Vic2, castille refusing to accept a white peace even though the war score is 99% in your favor but you just haven't taken that one colonial province in Africa, the inability of the US in Hoi 2 to properly handle nukes or how the Hoi2 AI in general assigns its generls
I don't think any of these flaws have prevailed but they were certainly huge atmosphere killers (at best and game breaking at worst) in the early versions of these games