Definitely not lack of sunlight, it's been in full sun since it was a little thing. Opuntiads.com also has photos of Opuntia ficus-indica that have pads that revert to ones that resemble O. streptacantha. I wonder if that sort of thing is happening with this one, or new root growth or location as you suggested. I didn't know that new root growth could cause the pads to change in such a way! I've seen single crested pads form on new plants before but have never seen every single new pad change or seen linguiformis type pads on an Opuntia ficus-indica until now.
