Hi jonathanexact,
It works fine for me. I tested on IE/firefox/chrome
1. I paste your code into editor normal view, it shows as below in html view.
<div>Header</div>
<div>Text</div>
<div>Text</div>
<div>Text</div>
2. Then Place cursor on first line and select <h1>, the code change to
<h1>Header</h1>
<div>Text</div>
<div>Text</div>
<div>Text</div>
All browsers gives me the same behavior
Regards,
Ken