To reproduce: 
Please refer to the attached sample application and video demonstrating the experience issue. 

Workaround: 
Set RadRichTextEditor to null in Form`s Dispose method: 
Protected Overrides Sub Dispose(ByVal disposing As Boolean)
    Me.RadRichTextEditor1 = Nothing
    Try
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
    Finally
        MyBase.Dispose(disposing)
    End Try
End Sub