Sounds like rodelization. In the wild, some female cannabis plants will naturally start making male pollen sacs or "bananas" which can self-pollinate the plant. This happens if the plant is stressed, or if the plant is not harvested in time and buds start to die of old age. The plant is basically doing everything it can to save the next generation. This method is "natural" and these seeds will all end up being mostly female, but the problem is you're selecting for plants that naturally hermie (grow both male and female sex organs) without any chemical induction. This means the resulting seeds are much more likely to turn hermie in natural conditions too. That's a problem if you don't want seedy buds every time you harvest. For that reason, it's highly recommended you don't feminize seeds this way, and it's a good idea to toss any and all seeds that are the result of natural herming.