Changing SqlDataSource.SelectCommand At Runtime Breaks Pagination?

I have a GridView bound to a SqlDataSource with a default SelectCommand defined as such:

<asp:SqlDataSource ID="SqlDataSource1" runat="server" DataSourceMode="DataSet"
ConnectionString="<%$ ConnectionStrings:MyConn %>"
ProviderName="MySql.Data.MySqlClient"
SelectCommand="select * from blah blah" />

There are cases where I have to change this query dynamically at runtime, so I do the following:

SqlDataSource1.SelectCommand = sql; // 'sql' is the new query
GridView1.PageIndex = 0;
GridView1.EditIndex = -1;
GridView1.SelectedIndex = -1;
GridView1.DataBind();
updatePanel.Update();

This works just fine actually, but when I click the pagination controls, the result set defaults back to the SelectCommand defined in the SqlDataSource1.