Changing User Control - Transparency

I am trying to create a user control that has a transparent background. I have this working, kind of. My problem is that I need this control to be able to change shape on the fly. This is what is happening.

The control is a simple filled rectangle or a simple elipse, based on a parameter. If I change the shape from a rectangle to an elipse, because the background is not being painted, the shape ends up with a retangle with an elipse on top (see attatched shape.jpg). If I put the form behind another app then bring it back to the front it looks fine.

How can I fix this so that it is tranparent but allows me to change the shape on the fly and repaint the entire control so the previous pixels don't remain and muck up the works?

Here is my code:

Code:

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Public Class Shape
    Private ShapeTypeValue
    Private Const WS_EX_TRANSPARENT As Int32 = &H20

    Public Enum Display
        None
        Rectangle
        Elipse
    End Enum
    Public Property ShapeType() As Display
        Get
            ShapeType = ShapeTypeValue
        End Get
        Set(ByVal value As Display)
            ShapeTypeValue = value
            Me.Refresh()
        End Set
    End Property

    Private Sub Shape_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
        If ShapeTypeValue = Display.Rectangle Then
            e.Graphics.DrawRectangle(Pens.Black, 0, 0, Me.Size.Width - 1, Me.Size.Height - 1)
            e.Graphics.FillRectangle(Brushes.LightGreen, 1, 1, Me.Size.Width - 2, Me.Size.Height - 2)
        ElseIf ShapeTypeValue = Display.Elipse Then
            e.Graphics.DrawEllipse(Pens.Black, 0, 0, Me.Size.Width - 1, Me.Size.Height - 1)
            e.Graphics.FillEllipse(Brushes.LightGreen, 1, 1, Me.Size.Width - 3, Me.Size.Height - 3)
        End If
    End Sub

    Protected Overrides ReadOnly Property CreateParams() As CreateParams
        Get
            Dim cp As CreateParams = MyBase.CreateParams
            cp.ExStyle = cp.ExStyle Or WS_EX_TRANSPARENT
            Return cp
        End Get
    End Property

    Protected Overrides Sub OnPaintBackground(ByVal e As PaintEventArgs)

    End Sub

    Public Sub New()

        ' This call is required by the Windows Form Designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.

        SetStyle(ControlStyles.SupportsTransparentBackColor, True)
        Me.UpdateStyles()
        Me.BackColor = Color.Transparent


    End Sub
End Class

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