Why does SharePoint Designer 2010 overwrite my SQLDataSource?

Why does SharePoint Designer 2010 overwrite my SQLDataSource?

I have a SharePoint page that uses a SPSqlDataSource to get data from SQL
Server. I noticed that an existing SharePoint page with similar function
had much better performance, and it used a SqlDataSource.
I replaced the SPSqlDataSource with a SqlDataSource, saved my changes,
tested the results, and found them superior to the SPSqlDataSouce. I
closed SharePoint Designer, and then things seemed to slow a bit. I opened
up my file and was surprised to find my updates had been overwritten, and
the original SPSqlDataSouce there.
How did my changes get overwritten? How do I make my change persistent?
<SharePoint:SPSqlDataSource runat="server" AllowIntegratedSecurity="False"
ConnectionString="Data Source=dbserver;
User ID=XXXXX;
Password=XXXXX;
Initial Catalog=XXXXX;
" ProviderName="System.Data.SqlClient" SelectCommand="SELECT ... FROM
... WHERE... " ID="BlueFolderPartsConnection1">
<SelectParameters>
<WebPartPages:DataFormParameter ParameterKey="AllParam"
PropertyName="ParameterValues" DefaultValue="*" Name="AllParam">
</WebPartPages:DataFormParameter>
</SelectParameters>
</SharePoint:SPSqlDataSource>
I changed it to this:
<asp:SqlDataSource
ID="BlueFolderPartsConnection1"
runat="server"
__designer:commandsync="true"
ProviderName="System.Data.SqlClient"
ConnectionString="XXXXX;
User ID=XXXXX;
Password=XXXXX;
Initial Catalog=XXXXX;
" SelectCommand="SELECT ... FROM ... WHERE... ">
<SelectParameters>
<WebPartPages:DataFormParameter ParameterKey="AllParam"
PropertyName="ParameterValues" DefaultValue="*" Name="AllParam">
</WebPartPages:DataFormParameter>
</SelectParameters>
</asp:SqlDataSource>