Weird!?

This isn't a problem so much as a bewilderment. I currently own four cats, and I've noticed that while 2 of them have no problem using the litterbox, they seem to miss it while scratching to cover their waste. One of them scratches outside the box while still standing in it, and the other actually scratches the wall next to it! Like I said, it doesn't cause any problem, but what on earth are they doing?

Avoiding the litter - one of mine has always done it - the instinct is there, but they don't really want to deal with the yucky (or scratchy part) I think, but who knows?!

Farley likes his business to be good and burried, he does scratch in the litter then all around the sides of the box, back into the litter then another round of the box walls etc.

Maia goes scratch cover nuts in her litter box! She digs a hole, then after shes done she covers it with litter and tries to fold over the litter box edges as well!!!! It sounds like she is hammering something and I know for a fact that sometimes she does it simply to wake me up I'll wake up when she starts and she runs out, didn't have to use it! Silly kitty!
She also scratch-covers her place mat sometimes, almost as if to cover her food or water bowel

My Gracie does that too.
She scratches forever to make a place to go, then digs and scratches the litter to cover it up.
Once it's covered she has a go at all four sides of the litter box and then for the grand finale she scratches the wall behind the box.

Our Boy Elliott digs to China before he goes, but WILL NOT cover...so sweet little Gracie hops into his litter box and goes through the whole routine to cover up her Brothers "deposit".