This is fixable, using the form-associated custom elements feature that's specified in HTML. (Introduction: https://html.spec.whatwg.org/multipage/custom-elements.html#...)

However, that's only currently shipping in Chrome, despite the other browsers being positive on it.

Similar capability gaps that we're working to close are accessibility (https://html.spec.whatwg.org/multipage/custom-elements.html#..., same situation, everyone likes it, only Chrome ships so far) and focusability (https://github.com/w3c/webcomponents/issues/762, still figuring out what the solution should be).