To reproduce:
- Add a scrollable panel wit other controls in a form.
- Show the form using the ShowDialog method.
- Scroll to the bottom the close and show the form again 
- You will notice that the scrollbar is not shown and the controls at the top are not visible.

Workaround:
Protected Overrides Sub OnClosing(e As System.ComponentModel.CancelEventArgs)
    MyBase.OnClosing(e)
    RadScrollablePanel1.VerticalScrollbar.Value = 0
End Sub