Viewstate - CheckBox Does Not Fire CheckedChanged Event When Unchecking?

I have a CheckBox on an ASP.NET Content Form like so:

<asp:CheckBox runat="server" ID="chkTest" AutoPostBack="true" OnCheckedChanged="chkTest_CheckedChanged" />

In my code behind I have the following method:

protected void chkTest_CheckedChanged(object sender, EventArgs e)
{
}

When I load the page in the browser and click the CheckBox it becomes checked, the page posts back, and I can see chkTest_CheckedChanged being called.When I then click the CheckBox again it becomes unchecked, the page posts back, however chkTest_CheckedChanged is not called.The process is repeatable, so once the CheckBox is unchecked, checking it will fire the event.I have View State disabled in the Web.Config, enabling View State causes this issue to disappear. What can I do to have reliable event firing while the View State remains disabled?Update:If I set Checked="true" on the server tag the situation becomes reversed with the event firing when un-checking the CheckBox, but not the other way around.Update 2:I've overridden OnLoadComplete in my page and from within there I can confirm that Request.Form["__EVENTTARGET"] is set correctly to the ID of my CheckBox.