Progmatically there is no bug, but as far as level design is concerned, yes there is. You see, one of the problems with this game's design is that the rust-colored key sprites are very small and often placed against rust-colored backgrounds in places which aren't logical locations for keys to be found in, so they're often difficult to find even when you're staring right at them.

Back when I originally played Redneck Rampage in the '90s, I could not find one of the keys on E1L7 (Smeltin' Plant). I must have spent at least an extra hour going back over every inch of the level before I finally gave up and cheated: I loaded the level into the editor and did a sprite search for the key. I found the tiny rust-colored key sitting in the corner of a not-small muddy patch of grass. There was no logical reason for a key to be found there and the lack of visual cues told my eyes that there was nothing there of interest, so I never noticed it during normal game play. If the level designer had set the key on something like a crate, the placement would have been reasonable, but as-is is just poor design.

That frustration was so strong that the memory has stuck with me all these years, so just before starting my recent play-through I edited the key's graphic by adding a non-diminishing green outline (doesn't darken in shadows or over distance).

I think there have been other times where I found the key by accident; I didn't realize where it was until I entered an area and saw "Skeleton key!" on my screen to indicate that I'd collected it.

This next bit contains spoilers:

Another problem with the poor level design is sometimes the player can't progress without finding mandatory secrets which are too well hidden, as in E2L7 (Beaudry Mansion). I don't remember how I beat the level a decade and a half ago, but when I recently played the level, I again had to cheat by doing a sprite search for the key in the level editor.

To get to the last key, you have go to [spoiler]a locked bedroom on the top floor where there's a switch on the side of a dresser. At a glance, it blends in with the dresser really well. To find the door it opened, you have to go down two long hallways and drop into the dining room. From there, you have to pass through the fireplace, as the back of the fireplace was the secret door that opened. Not only do the fire graphics do a very good job of obscuring this very small opening, but most clever players will have already looked there for a secret door and concluded that there isn't one. Also, the door and the switch are too far removed from each other for any sound effects to clue the player into where to look.[/spoiler] This would have been a really good, non-mandatory, ancient Chinese secret, but its discovery being mandatory in order for the player to progress is poor level design.