I have the same thing happening on two different strains: The one bladed leafs appeared a few weeks after I pinched the tops and clipped the tips off the big fan leafs to generate lateral growth. They look very healthy but they don't look like pot. Maybe it is some sort of evolutionary 'disguise' so that any animal programmed to eat five bladed plants wont nip at these plants any more.
From searching around for images this seems to happen often with dark green varieties: the one light green plant I have did not respond the same way and stayed normal.
In the end, how did your plants turn out?