Web Forms :: BoundField In Gridview Automatically Converts To Textboxes

When using a simple gridview targeting .net 4.0 if i click the edit button twice it converts to BoundFields to textboxes, but in previous version of .net (3.5 and 2.0) nothing happens (eventhough msdn says it suppose to happen). Have anyone seen this issue?

Code:
<asp:GridView ID="GridView1" AutoGenerateColumns="False" DataKeyNames="Id"
runat="server" onrowediting="GridView1_RowEditing">
<Columns>
<asp:BoundField DataField="Id" HeaderText="ID" Visible="False" />
<asp:BoundField DataField="FirstName" HeaderText="First Name" />
<asp:BoundField DataField="LastName" HeaderText="Last Name" />
<asp:TemplateField>
<ItemTemplate>
<asp:ImageButton ID="imageButton" AlternateText="Edit" CausesValidation="false" CommandName="Edit" runat="server" />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
public partial class _Default : System.Web.UI.Page
{
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }

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