Here's my binding source object:

Public Class MyListObject

    Private _mylist As New ObservableCollection(Of String)
    Private _selectedName As String

    Public Sub New(ByVal nameList As List(Of String), ByVal defaultName As String)

    	For Each name In nameList
    		_mylist.Add(name)
    	Next

    	_selectedName = defaultName

    End Sub

    Public ReadOnly Property MyList() As ObservableCollection(Of String)
    	Get
    		Return _mylist
    	End Get
    End Property

    Public ReadOnly Property SelectedName() As String
    	Get
    		Return _selectedName
    	End Get
    End Property

End Class

Here is my XAML:

<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300"
    xmlns:local="clr-namespace:WpfApplication1"
    	>

    <Window.Resources>
    	<ObjectDataProvider x:Key="MyListObject" ObjectInstance="" />
    </Window.Resources>

    	<Grid>

    	<ComboBox Height="23"
    			  Margin="24,91,53,0"
    			  Name="ComboBox1"
    			  VerticalAlignment="Top"
    			  SelectedValue="{Binding Path=SelectedName, Source={StaticResource MyListObject}, Mode=OneWay}"
    			  ItemsSource="{Binding Path=MyList, Source={StaticResource MyListObject}, Mode=OneWay}"
    			  />

    	<Button Height="23"
    			HorizontalAlignment="Left"
    			Margin="47,0,0,87"
    			Name="btn_List1"
    			VerticalAlignment="Bottom"
    			Width="75">List 1</Button>

    	<Button Height="23"
    			Margin="0,0,75,87"
    			Name="btn_List2"
    			VerticalAlignment="Bottom"
    			HorizontalAlignment="Right"
    			Width="75">List 2</Button>
    </Grid>
</Window>

Here's the code-behind:

Class Window1

    Private obj1 As MyListObject
    Private obj2 As MyListObject
    Private odp As ObjectDataProvider

    Public Sub New()

    	InitializeComponent()

    	Dim namelist1 As New List(Of String)
    	namelist1.Add("Joe")
    	namelist1.Add("Steve")
    	obj1 = New MyListObject(namelist1, "Steve")
.
    	Dim namelist2 As New List(Of String)
    	namelist2.Add("Bob")
    	namelist2.Add("Tim")
    	obj2 = New MyListObject(namelist2, "Tim")

    	odp = DirectCast(Me.FindResource("MyListObject"), ObjectDataProvider)
    	odp.ObjectInstance = obj1

    End Sub

    Private Sub btn_List1_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btn_List1.Click

    	odp.ObjectInstance = obj1

    End Sub

    Private Sub btn_List2_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btn_List2.Click

    	odp.ObjectInstance = obj2

    End Sub
End Class

When the Window first loads, the bindings hook up fine. The ComboBox contains the names "Joe" and "Steve" and "Steve" is selected by default. However, when I click a button to switch the ObjectInstance to obj2, the ComboBox ItemsSource gets populated correctly in the dropdown, but the SelectedValue is set to Nothing instead of being equal to obj2.SelectedName.

Thanks in advance!