`mr-button` and `mr-textfield` break if non-MRjs tags are present

[lobau]

Here is a pure MRjs markup. The textfield works and the button triggers the console.log() properly. → https://codepen.io/lobau/pen/MWxLwLx

If you introduce any other HTML tag in the markup, like a div or an h1, both stop working. → https://codepen.io/lobau/pen/KKEJpEr

Expectation is that MRjs can be mixed with standard markup and still work as intended.