I have a login form which uses an iframe to insulate the password from the rest of the app. All content both in the parent window and the iframe is loaded over https, however I'm still getting the "This content is not secure..." message. Why is this? The iframe is loaded with `sandbox="allow-forms allow-scripts"` eg. without Same-Origin (This is to prevent code running in the parent window introspecting the login form to find passwords). Could this be the cause of the problem? If so, is it intentional, could it be documented or fixed?