When the page is freshly loaded, click here:

This list should fill up with new content:

This fails in IE.
The HTML and script for the form above is: 

	<form method="get" action="#">
	
		When the page is freshly loaded, click here: 
		<button onclick="updateList(); return false;">Run Test</button>
	
		<br/><br/>
	
		This list should fill up with new content:
	
		<select id="TargetListID">
			<option value="3" selected="selected">First</option>
			<option value="4">Second</option>
		</select>
	
		<br/><br/>
	
		This fails in IE.
	
		<script type="text/javascript">
	
		//<![CDATA[
		function updateList(element, value) {
			new Ajax.Updater(
				'TargetListID',
				'newdata.html',
				{	
					method:'get',
					asynchronous:true,
					evalScripts:true,
					requestHeaders:['X-Update', 'TargetListID']
				}
			)
		}
		//]]>
	
		</script>	
	
	</form>
The complete contents of newdata.html (the page requested via AJAX) are: 
	
	<option value="1" selected="selected">Success! First</option>
	<option value="2">Success! Second</option>
What IE reports (via DebugBar 5.0.2) for the contents of the updated list is this: 

	Success! First</option>
	<option value="2">Success! Second</option>
The opening <option value="1" selected="selected"> tag is missing so none of the list renders.