I wish I knew, I seem to have the same problem. Someone at work says it means they aren't getting enough protein or something and I should take them off puppy food and give them the adult food (9mos), but I haven't checked with my vet yet.
On that note for those who know how acrobatic Alphy is, with his getting on my kitchen table. I came home last night and the little stink pot had pooped on my table!!!
gross!!!!!