Hi Dankworth,
I've done a fair bit of reading up online trying to find the actual genetic mechanism that caused this to occur and I've found one bit of info in a book called Hemp Husbandry:
4.9 ~ Sexual Expression
The sexual expression of cannabis is determined by its genetic makeup, and by its metabolic temper, which is regulated by the male enzyme andrase and the female enzyme gynase. Environmental conditions (light, nutrients, soil and water) may suppress the formation of the dominant enzyme, and allow the opposite sex to express itself partially (hermaphroditism)
or completely (sex reversal). (71, 72)
Here's a link:
http://www.rexresearch.com/hhusb/hh4bot.htm#HH49
So it would appear that stress of some kind causes the hormones andrase and gynase to to influence the sexual expression of the plant and they are talking about plants and not the potential sex of seeds so that is a bit of a clue right there methinks but I'm not a geneticist or cell biologist and want to write to a few big names in cannabis genetics to see if I can get some definitive answers as it's still a bit of a mystery and had someone told
me of such an occurrence I would have been highly sceptical but as I'm now finding cannabis gender most certainly is not
mainly down the the xx and xy chromosomes and looking in my copy of Advances Hemp Research by Paulo Ranalli a total of 12 intersexual forms of cannabis have been categorised and how they express sex has a lot to do with environment. (page 168 of Genetic improvement:conventional approaches)
But it's a fun mystery that has made me go out of my way to learn more about cannabis so it's all good and in response to your question, the clones were grown in a well dialled in environment and not seemingly stressed but then we are talking about a clone only strain that has been knocking about for 23 years and seeing as cannabis is only meant to live for a few months well then there is a huge source of stress right there.