My RB Pepper used to do this all the time and I always thought that it was strange behavior because Storm had never done it. Then when I adopted Sunny, he also began to do it. I was at a cat show one time and I noticed a Bengal cat doing this. I asked his owner about it and she said that it's normal cat behavior. In the wild, the cats will bury the rest of their uneaten food to save it for later. I told her that one of my cats never did this. She said that my Storm has probably become too domesticated. I never knew that a cat could become too domesticated.
I've also noticed Sky doing this too but not Cirrus. Cirrus is supposed to be more wild than my other cats because he was born to feral parents so this doesn't make sense to me.
At least I now know that it's normal behavior.