[2008] Drawing Panel background on Vista

[nmadd]

I have a custom Panel on which I'm drawing a gradient background and believe that I am missing something.

On Vista, I am noticing behavior that when I resize the form that contains the Panel by dragging either a side or top/bottom border, the Panel does not redraw correctly. However, when I resize by dragging the corner of the form, the Panel does redraw correctly. I don't believe I've observed this behavior on XP.

The code is pretty simple. Here is the meat of the drawing:

Protected Overrides Sub OnPaintBackground(ByVal e As System.Windows.Forms.PaintEventArgs)
    _gradientBrush = New LinearGradientBrush(Me.ClientRectangle, _
                                             _gradientBackground.StartColor, _
                                             _gradientBackground.EndColor, _
                                             _gradientBackground.LinearGradient)
    e.Graphics.FillRectangle(_gradientBrush, Me.ClientRectangle)
End Sub
 
Protected Overrides Sub OnScroll(ByVal se As System.Windows.Forms.ScrollEventArgs)
    Me.Invalidate()
End Sub

I've attached screenshots as well. Am I missing something that would cause this behavior? Thank you.