If it is not genetics you would have to assume environment...I wish I knew enough to offer an opinion of any value! I am very curious as to what the cause is. I have one photo, an HSO Bubba Kush and I thought she was odd with 9, 11 and 13 leaves, but discovered that was normal. I'm going to see what I can find out.
Edit: Spent some time googling (is that a word?). All I could find was either genetics, they called it "duck foot" after the plant of that name. Which we have ruled out due to the different strains involved. I did see one or two mentions of temperature and light, not enough of either. Don't know if that's of any help, hope so!