UpdatePanel and Placeholder Control Problem

Hello everyone,

I am having some problems with this page that has a Placeholder control inside an UpdatePanel control. When the updatepanel is triggered, then the page seems to do a full postback and I end up with 2 sets of controls added to the page instead of 1.

Here is where I'm creating the updatepanel and placeholder:
<asp:UpdatePanel ID="upd3" runat="server" UpdateMode="Conditional">
<ContentTemplate>
      <asp:PlaceHolder ID="plhSemesters" Runat="server" />
</ContentTemplate>
<Triggers>
      <asp:AsyncPostBackTrigger ControlID="btnSave1" EventName="Click" />
      <asp:AsyncPostBackTrigger ControlID="btnSave2" EventName="Click" />
</Triggers>
</asp:UpdatePanel>

Here is the code behind:
protected void Page_Load(object sender, EventArgs e)
{
      ...
      if (!IsPostBack)
      {
            //Enable Save Buttons
            btnSave1.Enabled = true;
            btnSave2.Enabled = true;
            //Set Course Title
            lblCourseTitle.Text = crs.courTitle;
      }
      //Display Semesters and each Location
      ArrayList sems = Semester.getSemesterList(DateTime.Now, sqlCon);
      DisplaySemesters(crs, sems, sqlCon);
      ...
}
private void DisplaySemesters(Course crs, ArrayList Semesters, SqlConnection sqlCon)
{
      //Go through each semester, and display all location frequencies
      plhSemesters.Controls.Clear();
      ...
      //TextBox for Course Frequency
      TextBox txtCFLoc = new TextBox();
      txtCFLoc.ID = "txt" + sem.semId + loc.locId;
      txtCFLoc.CssClass = "TextBox";
      txtCFLoc.MaxLength = 2;
      ...
      if (i % 2 == 0) { plhSemesters.Controls.Add(new LiteralControl("<tr class='ItemRow1'>")); }
      else { plhSemesters.Controls.Add(new LiteralControl("<tr class='ItemRow2'>")); }
      plhSemesters.Controls.Add(new LiteralControl("<td vAlign='middle' align='left' width='25%' class='LabelBold'>" + loc.locCity + "</td>"));
      plhSemesters.Controls.Add(new LiteralControl("<td vAlign='middle' align='left' width='10%'>"));
      plhSemesters.Controls.Add(txtCFLoc);
      plhSemesters.Controls.Add(new LiteralControl("</td>"));
      plhSemesters.Controls.Add(new LiteralControl("<td vAlign='middle' align='left' width='65%'></td>"));
      plhSemesters.Controls.Add(new LiteralControl("</tr>"));
      ...
}


When I click on one of the linkbuttons to trigger the updatepanel, I get a full page postback and 2 sets of controls.

Is there a bug with the updatepanel and placeholder controls or am I doing something wrong?