Hi bro, i had a bit of a hunt last night for info but as you say there's not much to back any of it up. I got that from a book called growing elite marijuana but it also points out hotter temps can do similar.
Here's my own take on this from years of growing regs. Some beans will always produce male or female, just like humans. Others will go one way or the other depending on the environment, pot size, nutrients etc.
If i'm right, the females i did get should be genetically stable and could possibly make good breeding stock. I'll need to remember to take some cuttings before they bud up.
The remaining plants are really going for it and will get very big so it's probably just as well i didn't get too many fems. The thing i hate most about growing regs is having to select which females to kill cos i don't have room for them all.