I have a cat, three now, who has recently started to launch herself out of her litter box after only mostly pooping. She then runs around the house or room she's in, frantically until the rest either comes out or falls off. It isn't often enough that I thought it was a health concern, but she didn't do it before. She's done it about three times in the last two months. Her stool looks 'normal,' and she doesn't seem to strain or be in pain when using the litter box.
M