According to the W3C spec, "A form control is disabled if its disabled attribute is set, or if it is a descendant of a fieldset element whose disabled attribute is set and is not a descendant of that fieldset element's first legend element child, if any." (See http://dev.w3.org/html5/spec-author-view/attributes-common-to-form-controls.html#attr-fe-disabled for more information). If a form element is a descendant of a fieldset with attribute 'disabled', it is still displayed as enabled. Here is an example of HTML that exhibits the bug: <fieldset name="clubfields" disabled> <legend> <label> <input type=checkbox name=club onchange="form.clubfields.disabled = !checked"> Use Club Card </label> </legend> <p><label>Name on card: <input name=clubname required></label></p> <p><label>Card number: <input name=clubnum required pattern="[-0-9]+"></label></p> <p><label>Expiry date: <input name=clubexp type=month></label></p> </fieldset> (See http://dev.w3.org/html5/spec-author-view/the-fieldset-element.html#the-fieldset-element for more information on expected behavior).