IE11 and Edge don't get value of checkbox when submitting form

This returns null on IE11 and MS Edge, but returns 'yes' on Chrome and Firefox:

$insuranceChecked = Mage::app()->getRequest()->getPost('insurance');
var_dump($insuranceChecked); die;

This is the checkbox input field:

<input id="insurance" type="checkbox" name="insurance" value="yes" form="product_addtocart_form">
<label for="insurance"></label>

Any idea why? I really need to fix this ASAP.