Because the default search action of web app search forms is to search partial words, if you specify MALE then FEMALE will be included in the result.
Buried in the description for how a Web App works is an instruction regarding using a custom field for Gender in your web app.
To avoid this issue on your search page, add this text to the end of your form’s Action URL:
&Exact=true
On my site the Ampersands were coded into the URL as &
example:
&Exact=true
