"ComboBox contains no items" error triggered when selecting item from combobox in coded step

I'm attempting to use a coded step to do a series of actions, including selecting an item from a silverlight radcombobox.  I can record/playback this exact scenario without any problems, but when I attempt to do the exact same thing through code I get the following error:

Error:
System.ArgumentException: ComboBox contains no items to search in and select! Please make sure the test case opens the drop down first.

Code Snippet #1 that caused error:
comboBox.SelectItem("TEST", true);  //this should both open and select the TEST item from the comobox

Code Snippet #2 attempting to workaround, the same error is triggered:
comboBox.User.Click(); //Open combobox manually
System.Threading.Thread.Sleep(5000); //Manual wait, just in case it was a speed issue
comboBox.SelectItem("TEST", false); //select the TEST item from an open combobox

Code Snippet #3 attempting to workaround, no error is triggered as the foreach is skipped because there are zero items found:
comboBox.User.Click(); //Open combobox manually
System.Threading.Thread.Sleep(5000); //Manual wait, just in case it was a speed issue
foreach (Telerik.WebAii.Controls.Xaml.RadComboBoxItem rcbi in comboBox.ItemElements) //attempting to loop through all items in combobox
{
   if (rcbi.ToString() == "TEST")
     {
         rcbi.User.Click();
     }
}

Copied from DOM:
<radcombobox Name="comboBox" AutomationId="comboBox" Uid="30481338">
  <grid Name="VisualRoot" Uid="3226344">
    <border Uid="16841414" />
    <radtogglebutton Name="PART_DropDownButton" AutomationId="PART_DropDownButton" Uid="33647865">
    </radtogglebutton>
    <validationtooltip Name="ValidationTooltip" BaseType="Control" Uid="34395333" />
    <popup Name="PART_Popup" AutomationId="PART_Popup" Uid="45097725">
      <grid Name="PopupRoot" Uid="43140557">
        <shadowchrome BaseType="Control" Uid="41122544">
        <border Name="PART_ResizeBorder" Uid="27380479">
          <grid Uid="47781518">
            <radbutton Name="PART_ClearButton" AutomationId="PART_ClearButton" Uid="34558579" />
            <scrollviewer Name="PART_ScrollViewer" AutomationId="PART_ScrollViewer" Uid="42591759">
              <border Uid="65381771">
                <grid Uid="14721181">
                  <scrollcontentpresenter Name="ScrollContentPresenter" Uid="10290070">
                    <itemspresenter Uid="51565033">
                      <stackpanel Uid="61432121">
                        <radcomboboxitem Uid="16018178">
                          <border Uid="309837">
                            <grid Uid="51795644">
                              <border Name="HighlightVisual" Uid="21433500">
                                <border Uid="58683773" />
                              </border>
                              <contentpresenter Name="Content" Uid="63507614">
                                <grid Uid="43843091">
                                  <textblock Uid="34697616">TEST</textblock>


Am I missing something?