Why DetailsView.ChangeMode method does not fire ModeChanging and ModeChanged events? - asp.net

Question

I have an ASP.NET WebApplication page with DetailsView bounded to SqlDataSource.
When I try to change mode by auto-generated Edit or Insert buttons, events are fired.
When I try to change mode programmatically by DetailsView.ChangeMode method call (inside custom button click), ModeChanging and ModeChanged events are not fired.
Why it does not work ?
There is aspx listing:
<form id="form1" runat="server">
<div>
<h1><asp:Label ID="Label" runat="server" Text="ReadOnly" /></h1>
<asp:DetailsView ID="DetailsView" runat="server"
DataSourceID="SqlDataSource"
EnableModelValidation="True"
AllowPaging="True"
AutoGenerateEditButton="True"
AutoGenerateInsertButton="True"
OnModeChanged="DetailsView_ModeChanged">
<FooterTemplate>
</FooterTemplate>
</asp:DetailsView>
<asp:SqlDataSource ID="SqlDataSource" runat="server"
ConnectionString="<%$ ConnectionStrings:PEMDConnectionString %>"
SelectCommand="SELECT * FROM [evd].[WaterTemplates]"
InsertCommand="INSERT INTO [evd].[WaterTemplates] (TemplateName,TemplateDescription) VALUES (#Name,#Description)" />
<asp:Button ID="InsertByChangeModeButton" runat="server"
OnClick="InsertByChangeModeButton_Click"
Text="Insert By ChangeMode" />
<asp:Button ID="EditByChangeModeButton" runat="server"
OnClick="EditByChangeModeButton_Click"
Text="Edit By ChangeMode" />
</div>
</form>
and here is code behind:
namespace WebApplication1
{
public partial class _Default : System.Web.UI.Page
{
protected override void OnPreRender(EventArgs e)
{
base.OnPreRender(e);
switch (DetailsView.CurrentMode)
{
case DetailsViewMode.Edit:
case DetailsViewMode.Insert:
EditByChangeModeButton.Visible = false;
InsertByChangeModeButton.Visible = false;
break;
case DetailsViewMode.ReadOnly:
InsertByChangeModeButton.Visible = true;
EditByChangeModeButton.Visible = true;
break;
default:
break;
}
}
protected void InsertByChangeModeButton_Click(object sender, EventArgs e)
{
DetailsView.ChangeMode(DetailsViewMode.Insert);
}
protected void EditByChangeModeButton_Click(object sender, EventArgs e)
{
DetailsView.ChangeMode(DetailsViewMode.Edit);
}
protected void DetailsView_ModeChanged(object sender, EventArgs e)
{
switch (DetailsView.CurrentMode)
{
case DetailsViewMode.Edit:
Label.Text = "Edit";
break;
case DetailsViewMode.Insert:
Label.Text = "Insert";
break;
case DetailsViewMode.ReadOnly:
Label.Text = "ReadOnly";
break;
default:
break;
}
}
}
}