Perhaps the items retrieved contain m/f as well as M/f?
When searching, make sure you click teenand child but NOT adult; alternatively, enter m/f in the orientation field.
Note also that searching m/f isn't ideal because it won't pull out other permutations, such as m/mf etc
There's a section in Help on searching that yuou might find useful. You'll find it here:
http://www.thespankinglibrary.org/index.php?func=help
