Probably an f1 or f2 variation of sorts would be my first guess. Likely from an f1 source.
Doesn't mean anything really, IMO, just means your going to have 2 different phenos from the same seed stock.
It happens.... Once you get stocks to a f3 state there "supposed" to not do that anymore.
It's a real obvious phenomena that occurs especially when crossing breeding Autos IMO. I've even seen one bean be auto, and the next photo-period. I've got a really massive f1 sativa auto that looks like it fits in that category right now, but that doesn't keep me from growing it.
The other thing I would check is making sure there all getting that morning/mid/evening sunlight in a uniform fashion. That somehow one of the plants isn't blocking the others (especially the budding ones) from getting full sunlight.