Child Objects and Undo

Hello,

I have an issue regarding child objects and undo. Undo doesn't work for child objects like:

 Public Shared ReadOnly VatRateProperty As PropertyInfo(Of VatRate) = RegisterProperty(Of VatRate)(Function(c) c.VatRate, RelationshipTypes.Child)

    Public Property VatRate() As VatRate
        Get
            Return GetProperty(VatRateProperty)
        End Get
        Set(ByVal value As VatRate)
            LoadProperty(VatRateProperty, value)
        End Set
    End Property

I'm assuming that the undo mechanism saves the reference of the object rather than the object itself. How can I overcome this problem?

p.s.: I'm not using the dataportal. I have my own classes for getting/saving data in mysql.