Strain
This played out exactly like another photo period I grew the year before. I bought it as a clone and it was already growing for at least 3 weeks. This was back in late May (approx) - and it was outside for a good 5 months, maybe a bit more. When the heat kicks in here, any photo period that's been going for so long will just mess up.
I have had great success with photo periods - but they have to be germinated around late June. They just can't handle the prolonged heat and go haywire. This one produced hundreds of bud sites, but they were all really, really, small. Exactly the same the plant I grew the year before (an O.M.G. from Ripper Seeds)
It's not the seeds, it's the climate and timing.
But all was not lost, the buds were a pain to harvest but they were incredibly sticky - so I turned into some lovely bubble hash and gave the rest of the flower away.