There are some very experienced breeders on this site that can tell you why feminized cannabis seeds sometimes become hermaphrodites (and I'm assuming by week 4 that your plant has produced pistels at the bud sites?).
I've read a little about it - something about F2s and F4s - but most of it is over my head - ha ha!
What I have gleaned is that feminized seeds are often a little unstable (which may be why many of the most experienced growers plant unfemed seeds, and cull the males) - and can become hermaphrodites with or without stress factors (temp, humidity, transplant, nutrient deficiency/toxicity).
The Hobbit I currently have underway also produced pollen sacks - low down on his/her stem that I didn't notice under the fan leaves until after they had opened and dropped their payload.
As she was the only plant I had in flower - I kept on with her, and she produced three seeds (that I can see) on her bud sites.
Anyway - I'm sure someone that knows what their talking about will chime in here - but in summation, from what I've read, feminized seeds are just a little unstable like that.
I believe the Kinks said it best:
"Girls will be boys and boys will be girls
It's a mixed up muddled up shook up world except for Lola
Lo-lo-lo-lo Lola "