isEnabled() always returns true - protractor

there are couple of checkboxes. i am trying to test the first checkbox is enabled or disabled.

my html is -

<md-checkbox ng-change="$ctrl.onDnbStatusChange(result)" 
ng-disabled="result.status == 'Deny'" aria-label="Checkbox" 
ng-model="result.dnb" role="checkbox" 
class="ng-valid md-blueTheme-theme ng-dirty ng-valid-parse ng-touched 
ng-empty" tabindex="-1" aria-disabled="true" aria-checked="false" aria-invalid="false" 
disabled="disabled">

i am using this command to test it- the problem is, it always returns true even though the checkbox is disabled.

expect(element.all(by.model('result.dnb')).get(0).isEnabled()).toBe(false);

any suggestions.

thanks.