WCF trace logs all exceptions except System.Exception itself - wcf

Question

I've made a basic WCF Service Library and created one method called GetResult(). I've set up WCF trace logging to log Warnings to a file. This is correctly logging all exceptions thrown except, for some strange reason, System.Exception itself. For instance, this logs fine:
[OperationContract]
public string GetResult()
{
// exception is logged in file:
throw new DivideByZeroException();
// or
// throw new ApplicationException();
// or
// throw new FileNotFoundException();
// or anything else, it seems
}
But this does not log anything:
[OperationContract]
public string GetResult()
{
// exception is not logged!
throw new Exception();
// or
// throw new Exception("my message");
}
In the latter case, the log file doesn't even get created. If it already exists then it doesn't get written to.
What am I doing wrong?
Here is my app.config setup:
<system.diagnostics>
<sources>
<source name="System.ServiceModel.MessageLogging" switchValue="Warning">
<listeners>
<add name="ServiceModelTraceListener" />
</listeners>
</source>
<source name="System.ServiceModel" switchValue="Warning">
<listeners>
<add name="ServiceModelTraceListener" />
</listeners>
</source>
<source name="System.Runtime.Serialization" switchValue="Warning">
<listeners>
<add name="ServiceModelTraceListener" />
</listeners>
</source>
</sources>
<trace autoflush="true" />
<sharedListeners>
<add initializeData="c:\temp\logs\wcf.svclog"
type="System.Diagnostics.XmlWriterTraceListener, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
name="ServiceModelTraceListener"
traceOutputOptions="Timestamp" />
</sharedListeners>
</system.diagnostics>