Ive had this happen before in a 70/30 (sativa/indica) at week 8 of flowering ... This is not a hermie however, rather they are called intersex flowers and Skitzofrantic is right about them being a last-ditch survival mechanism for a female plant in its last weeks. The bad news is that the pollen from these, while not as much so as from a male or hermie, is quite viable and may seed your crop. The good news is that any resultant seeds will technically be feminized due to the fact that the only possible chromosomes passed on will be y (female).
The only difference between this type of feminized and a commercial feminized seed is that most companies use a male hormone spray such as Stamen-it! to produce male flowers on females (plant stress is also a stimuli to grow male flowers.. probably what happened in your case by accident)
fyi, I tested this theory when buds of mine grew male flowers and I ended up with about 24 seeds (in about a hp of some bubonic chronic!) Those seeds had a germination rate of 60% (my fault bc I let some dry out after they cracked =( ) and were all female!
If you dont want any seeds, wear disposable gloves and use tweezers to pluck them out while your crop matures. It is a good idea to spray them with a fine mist of water to prevent pollen from going everywhere. You will probably miss a few, as I did, but so what you will get some free Fem. seeds mahfucker!!!
