Checkbox with javascript unexpectedly unchecks other checkboxs

Hi,

I have a checkbox called applicant_isemailaddress which has onchange javascript

if (this.rawValue) {Page1.doYouEmail.presence = "visible";Page1.applicant_allEmailAddresses.presence = "visible";}else {Page1.doYouEmail.presence = "hidden";Page1.applicant_allEmailAddresses.presence = "hidden";};

when checkbox applicant_isemailaddress goes to the "on" state, then two other checkboxs on the page get unchecked.

they are called applicant_isMaleSex and applicant_isFemaleSex, I've tried changing the names to no benefit.

removing the above javascript fixes the behaviour

whats the trick??

tia.

Brian