Yeah, it's the reason I started looking up official answers to some unusual occurrences like the ones mentioned before.
The only one that actually caused a momentary stop in gameplay with my group is the more common one, resilient vs ammo, but we agreed the wording on the ammo card trumped the discarding of the gun, thematically makes sense, unloading a full clip into a stubborn zed, "damn that was close, bastard wouldn't go down, better reload".
The instant kill one I was very confused about and not sure which side of the fence was right, I had read this argument and participated in it, but it was this post by Mr. Jason C. Hill that helped clarify things for me.
http://boardgamegeek.com/article/6751865#6751865
So while we can fault FFP for not being all that clear on the intent of the rules (I'd say more confusion comes from the cards, as the rulebook do a slightly better job of explaining effects) I still give Hill & his staff brownie points because they take it upon themselves to post answers to problems caused by iffy wording and expansions.
So if I'm understanding Mr Hill correctly:
Jade rolls 6-1-1 against Barbed Wire Zombie
Result: Zombie wins, Jade can't re-roll but avoids wound.
Jade equipped with Cleaver/Shears rolls 6-1-1 against Barbed Wire Zombie
Result: Jade wins, kills zombie, avoids wound.
If she had rolled 6-1 she'd kill it but take 1 wound for losing fight (Zombie clawed her just as she brought the cleaver down on it's head for the kill)
If it were Rachelle, then she can ALWAYS roll for intuition of every single wound she would take regardless if it's in a fight or not. (That's why a love that Rachelle + Police Vest Combo, she becomes UBER TANK! But if the dice fail her she can still die)
And Sally, well she isn't so Lucky after all, if she's being affected by an Instantly Killed/Lose.