Over the years I've had a few cats who would do this. When I put clean litter in the litter pan, they would get excited and go jump in it and flip and roll around in it. Since they do it only for a short time and only when the litter pan has fresh clean litter in it, I never considered it a problem. I've seen some cats who would roll in clean garden soil the same way. Cats are a species that don't care much for getting wet.Maybe the clean litter/clean garden soil rolling behavior of some cats is related to behaviors such as those of birds who dust bathe or Chinchillas who bathe in lava dust but never bathe in water.