New Post: CheckListBox not showing data

I've created a User Control with a CheckListBox and when the Control is displayed, there is no data visible. I have verified that the CheckListBox items have the contents that were added, but the display has unchecked boxes and no text. What am I missing?

This is the XAML:
<UserControl x:Class="frmMatlList"

         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"              
         mc:Ignorable="d" Height="259" Width="478">
<Grid>
    <xctk:CheckListBox x:Name="lbMatlList" 
                        Height="250"
                        Width="400"
                        DisplayMemberPath="TheText"
                        ValueMemberPath="TheText" 
                        SelectedMemberPath="IsSelected"
                        SelectedValue="{Binding TheText}"
                        Delimiter="|"
                        SelectedItemsOverride="{Binding SelectedItems}" >
    </xctk:CheckListBox>
....

The VB code that inserts data is:

    Me.lbMatlList.Items.Clear()
    iMatls = 0
    For iNum = 1 To MatlList.LongCount
        tString = MatlList(iNum - 1)
        ' Check whether this entry should be checked
        Used = ContainsLabel(tString, SelMatlList) 
        Me.lbMatlList.Items.Add(New Used_Material(Used, tString))
        Dim MatlItem As Used_Material = Me.lbMatlList.Items(iMatls)
        iMatls += 1
    Next iNum

with Class:
Class Used_Material

Public IsSelected As Boolean
Public TheText As String
Public Sub New(ByVal tmpUsed As Boolean, ByVal tmpName As String)
    IsSelected = tmpUsed
    TheText = tmpName
End Sub

End Class