One thing that you may be dealing with is the serialization as you mentioned. If you have a collection, then you will want to assign the Content tag through the DesignerSerializationVisibility property. Like this:
Public Class MyTest
<DesignerSerializationVisibility(DesignerSerializationVisibility.Content)> _ Public Property MyProperty() As MyCollection Get
End Get Set(ByVal value As MyCollection)
End Set End Property
End Class
This might get you going in the right direction or at point you towards another attribute that would help. The above tag can be used to just ensure that the serialization is visible as well.