Re: goes to the bathroom, then scratches. forever.
Mine do that, too... they scratch at the sides of the box, at the wall, at the side of the washing machine next to the box... and then walk off, satisfied that they've done their duty, while the poop remains uncovered.
Sometimes the other will come along, see the unburied poop, and then feel obliged to bury it... which, you guessed it, she'll do by scratching at the side of the box (sometimes the OUTSIDE ofthe box) or the wall.
They were apparently turned in along with their mother and their mother's next litter, so they weren't taken away from Mom too young, either. I can't explain it.
Have you tried different kinds of litter? While I was experimenting with brands I found they were more prone to bury in some litters than others, and I find that when I use the Feline Pine (pine pellets) they bury more towards the end of the week when the pellets have mostly gone to sawdust. From that I'm guessing I could encourage them to bury by switching to a finer-grained litter, but I like the Feline Pine for other reasons so I've just resigned myself to frequent scooping to keep the smell down.