It is actually pretty normal...a bunch of my friends and I all thought we had "special" kitties until we found out all of our cars did it....15 different cat households all doing the same thing....we decided it was a Kitty Cat Conspiracy instead...lol.
Hey, who wouldn't want to use a freshly cleaned litterbox? My furbabes do that all. the. time. Drives me nuts. I usually clean them, wait five minutes, and clean them again. Heaven forbid I have spotless litter boxes..