title: WCF Enum issue: cannot "or" the enum values
body: <p>I use enum as flags and wants to "or" it, but always meet a error:</p>
  
  <p>Enum value '3' is invalid for type 'Common.EventType' and cannot be serialized. Ensure that the necessary enum values are present and are marked with EnumMemberAttribute attribute if the type has DataContractAttribute attribute</p>
  
  <p>code:</p>
  
  <pre><code>[DataContract]
  public enum EventType
  {
      [EnumMember]
      Event1 = 1,
      [EnumMember]
      Event2 = 2,
      [EnumMember]
      Event3 = 4,
      [EnumMember]
      AllEvents = Event1 | Event2 | Event3
  }
  </code></pre>
  
  <p>MyContractClient proxy = new MyContractClient(context);</p>
  
  <p>proxy.Subscribe(<strong>EventType.Event1 | EventType.Event2</strong>);</p>
  
  <p>Thank you in advance</p>