fetch_params returns "yes" instead of "y" and "on" (and "no" instead of "n" or "off")

$my_string = $this->EE->TMPL->fetch_param('my_param') ;

{exp:my_pi my_param="y"} tagdata {/exp:my_pi}

If my_param is “y” or “on” then $my_string evaluates to “yes”.

If my_param is “n” or “off” then $my_string evaluates to “no”.

If my_param is “N” or “Y” or “ON” or “OFF” or anything else then $my_string evaluates to my_param.

Is this the intended behavior? Is there any way to turn it off so EE won’t mess with my parameter strings?