The case would be that they are not 100% bred correctly or you growing conditions.
Hermaphrodite tendency is largely a matter of genetics. Either your strain has that tendency, or it doesn't. Stress/shock just makes plants otherwise susceptible to doing this actually do it.
Ive Made Plenty OF Hermies Before! I know It also Can be Stress / Light Cycle Related.
But Thats How they make A Femanized Seed is Hermi Breeding ~ So if Its a Femannized Seed IT COMES FROM A HERMI Program ~ Take a LOOK
http://www.cannabisculture.com/node/394
Heres a Link to good Forum That goes into Detail ~
http://forum.grasscity.com/cannabis-seeds-banks/212862-info-feminized-seeds.html
I Still Use Femanized Seed From Time To Time ( Freebies) ~ They Also Can Prduce Some Great Bud. For Sure!
But
If I was Gonna Pay Money tho ~ Id Buy Regular Seeds
In a 12 pack ur gonna get a Some Females~ Clone all 12 2x Once rooted & 15 days grow 24 or 18/6 light cycle
I Throw 24 rooted clones into bud 12/12 for Sexing on the 12 Pack in Grow ~ Usally Around 60% is what I get For Females ~ Sometimes higher
Cull out males Bud out 2 clones of Each Female ~ I usally Keep the Plant from Seed as My Mother.
So I try & not bud out Seeded Plant Until I know Which one I wanna Keep for mothers ~ If That Makes Sense?
This Takes A long time To do~ If your IN a Hurry Just Buy Female Seeds ~
but If your Into Growing Strong Gentics & having A Great Mother that u know is gonna Be a Great Plant to take clones from Time after time I Suggest Growing a 12 Pack of The Strain & Finding Her Best Genes
One Seed Isnt Gonna Even Show you What That Strain Can Throw Trait Wise
U have to Grow out At least 6-12 from seed to See Diffrent Gentics of that Breed
but Some Strains Will Takes 100's Seed To See All the Traits.
Hope this Helps ~