ASP.NET ​ObjectData​Source caching

So I'd love to move to using the built-in data caching of the ObjectDataSource, but I'm hitting a snag.

If I use basic types for my session parameter, changing the value triggers a cache refresh.

Session["myValue"] = 5; //data loaded from the database

Session["myValue"] = 15; //data loaded from the database

If I use custom types for my session parameter, changing the value does not trigger a cache refresh.

Session["myValue"] = new MyCustomObject(5); //data loaded from the database

Session["myValue"] = new MyCustomObject(10); //data loaded from the cache

I've overridden my Equals method to always return false, yet the data still loads from the cache every time.

Any ideas?

Further weirdness:

If I override the ToString method in my custom class, and have it return the parameter, then the cache is used properly.

This works:

<Serializable()> _
Public Class MyType
    Public Property Value As String

    Public Sub New(value As String)
        Me.Value = value
    End Sub

    Public Overrides Function ToString() As String
        Return Me.Value
    End Function
End Class

This doesn't:

<Serializable()> _
Public Class MyType
    Public Property Value As String

    Public Sub New(value As String)
        Me.Value = value
    End Sub
End Class

Shouldn't ObjectDataSource be using the Object.Equals() method to determine if the select parameter is different, and not the string representation?