The Current SVN "Rev90" has line 1207 of cGirls.cpp
if (current->m_YourDaughter == 0) AddTrait(newGirl, "Your Daughter");
This seems to be a check against the new YourDaughter Status, which is then adding the trait for 0. 0 in this instance means false or no, I believe.
I think it was an accident, since right above it's checking the same kind of check, but it's a human check, and adding "not human". That would mean this would have to be "not daughter".
This explains why I kept having the slave market propagated by my daughters. For some odd reason, this didn't make every single one to be out that way, but a random amount. I don't know why.
Switching the 0 to a 1 eliminates the random daughters.