Use of undefined keyword value 1 for event TaskScheduled

Question

When debugging my universal Windows (8.1) app i encounter the following error from time to time:

System.ArgumentException was unhandled
  _HResult=-2147024809
  _message=Use of undefined keyword value 1 for event TaskScheduled.
  HResult=-2147024809
  IsTransient=false
  Message=Use of undefined keyword value 1 for event TaskScheduled.
  Source=mscorlib
  StackTrace:
       at System.Diagnostics.Tracing.ManifestBuilder.GetKeywords(UInt64 keywords, String eventName)
       at System.Diagnostics.Tracing.ManifestBuilder.StartEvent(String eventName, EventAttribute eventAttribute)
       at System.Diagnostics.Tracing.EventSource.CreateManifestAndDescriptors(Type eventSourceType, String eventSourceDllName, EventSource source)
       at System.Diagnostics.Tracing.EventSource.EnsureInitialized()
       at System.Diagnostics.Tracing.EventSource.SendCommand(EventListener listener, Int32 perEventSourceSessionId, Int32 etwSessionId, EventCommand command, Boolean enable, EventLevel level, EventKeywords matchAnyKeyword, IDictionary`2 commandArguments)
       at System.Diagnostics.Tracing.EventSource.OverideEventProvider.OnControllerCommand(ControllerCommand command, IDictionary`2 arguments, Int32 perEventSourceSessionId, Int32 etwSessionId)
       at System.Diagnostics.Tracing.EventProvider.EtwEnableCallBack(Guid& sourceId, Int32 controlCode, Byte setLevel, Int64 anyKeyword, Int64 allKeyword, EVENT_FILTER_DESCRIPTOR* filterData, Void* callbackContext)

I can then skip this error and am able to proceed using the app in debug mode but when installed on a device the app will crash. I have searched for an answer for some time now but the only answer i have come across here is to disable breaking on these kind of exceptions which is of course not a very good answer.

Thanks in advance.

EDIT 1: Ok, i have a very simple sample project with which this error is easily reproduced. I created a Universal App Blank app in Visual Studio 2013 Ultimate and added the following code to the App.xaml.cs. The exception posted above is raised on the line with await. Can anybody help because this is plagueing me for months now.

public App()
{
  this.InitializeComponent();
  this.Suspending += this.OnSuspending;

  callService();
}

async public Task callService()
{
  string url = "http://eu.battle.net/api/d3/profile/bunnynut-2128/";
  HttpClient client = new HttpClient();
  string data = await client.GetStringAsync(url);
  client.Dispose();
}