The dictionary <struct, int> is not ordered properly

I have a WCF service and am trying to send Dictionary<CustomStruct, int>from my client to my server. My WCF service uses a standard base binding.

When I send the dictionary to the server, an error does not occur. But when I try to focus on my dictionary, it is empty.

Strange, what Dictionary<string, string>really works ?!

Does anyone have an idea why mine is Dictionary<CustomStruct, int>empty after it passes through the wire and why it works Dictionary<string, string>.

[EDIT] This is what my structure looks like:

[DataContract]
public struct CustomStruct : IEquatable<CustomStruct>
{
    [DataMember]
    private string _prop;

    public string Prop { get { return _prop; } }

    public override int GetHashCode()
    {
        return Prop.GetHashCode();
    }

    public static bool operator ==(CustomStruct left, CustomStruct right)
    {
        ...
    }

    public static bool operator !=(CustomStruct left, CustomStruct right)
    {
        ...
    }

    public override bool Equals(object obj)
    {
        ...
    }
}