El editor de codemirror no carga contenido hasta que hace clic

Solo hay que agregar autorefresh.js     

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/codemirror.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/mode/javascript/javascript.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/mode/css/css.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/mode/xml/xml.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/addon/selection/active-line.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/addon/edit/matchbrackets.min.js"></script>


<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/addon/display/autorefresh.js"></script>


<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/codemirror.min.css"/>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.28.0/theme/abcdef.css"/>

Y en el script:  autoRefresh:true,

<script type="text/javascript">	
  $(document).ready(function(){
	var code = $(".codemirror-html")[0];
	var editor = CodeMirror.fromTextArea(code, {
	  lineNumbers : true,		
    tabSize:3,
    styleActiveLine: true,
    theme:"udb-dark",
    matchBrackets: true,
	autoRefresh:true,	
    mode: "text/html"		
	});
});

</script>

Referencia

http://js.dokry.com/el-editor-de-codemirror-no-carga-contenido-hasta-que-hace-clic.html