one of my kittens does the same thing!! he really likes to lay in the litter. he will just sit in it. he doesnt appear to be struggling, and its definatly not that he is squating... i think he just likes the feel of the litter... maybe it is comforting?
all of my kittens and thier mom tend to be messy with the litter, their mom loves to kick it out of the box, and i have one of the huge rubbermaide ones, and then a smaller one in another room. she does it worse ont he smaller one, but still does it occasionally with the bigger one. *shrug* sometimes i think she does it to just get on my nerves lol.