Created Unassigned: Cannot clear HTML Editor Extender [27464]

I'm using ACT 4.1.7.607. Client is IE 9.

I can not find a solution where I can clear the contents of the editor from the client.

I have tried using JQuery:
<asp:TextBox ID="TextBox1" runat="server" TextMode="MultiLine" height="200px" Width="837px"></asp:TextBox>
<ajaxToolkit:HtmlEditorExtender ID="htmlEditorExtender" TargetControlID="TextBox1" runat="server" EnableSanitization="False"></ajaxToolkit:HtmlEditorExtender>
<br />
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Submit" />
<asp:Button ID="Button2" runat="server" Text="Clear" />

<script type="text/javascript" language="javascript">
$(document).ready(function () {
$('#<%=Button2.ClientID%>').click(function () {
var editorControl = $get("<%=TextBox1.ClientID%>");
var clearValue = '';
editorControl.innerHTML = clearValue;
})
})
</script>

This seems to change the innerHTML value of the textbox. However, the screen does not update to show the change.

Have also tried JavaScript:

<asp:TextBox ID="TextBox1" runat="server" TextMode="MultiLine" height="200px" Width="837px"></asp:TextBox>
<ajaxToolkit:HtmlEditorExtender ID="htmlEditorExtender" TargetControlID="TextBox1" runat="server" EnableSanitization="False"></ajaxToolkit:HtmlEditorExtender>
<br />
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Submit" />
<asp:Button ID="Button2" runat="server" Text="Clear" OnClientClick="javascript:clearEditor()" />

<script type="text/javascript" language="javascript">
function clearEditor(){
document..getElementById('<%=TextBox1.ClientID%>').innerHTML = '';
}
</script>

This also seems to change the innerHTML value, but, again it does not show the change in browser window.

If there is a solution to this, I would be most grateful to see it.