Deserializing of List Array appends instead of overwrite

[Wild Thing]

Hi, I am using a list of a class. Serialization works fine, but Deserialization leads to creating new lists, which are appended to main list. I.e. if Deflists in AllKeyList contains 5 KeyDefinition Classes, after Deserialization there are 10. How can I force overriding? Thx adv for your help. What I'm doing:

        FileStream fs = new FileStream(sFile, FileMode.Open);
        var x = new System.Xml.Serialization.XmlSerializer(Setup.GetType());

        var settings = new XmlReaderSettings { CheckCharacters = false, };
        try
        {
            Setup = (DataSettings)x.Deserialize(fs);
            Console.WriteLine("XML Read {0} erfolgreich", sFile);

Data structure:

public class KeyDefinition
{
    public string Name { get; set; }
    public string KeyType { get; set; }
    public List KeyDef { get; set; }
    ....
}

public class AllKeyList
{
    public List DefLists { get; set; }
    ...
}

[kdbueno]

array list, are working in methods, of acceptance, but not equivalent static and kinetic algorithmics works well with ibm datastage, for instance, nor ibm infosphere.