Tests using log4net run very slowly

I've recently been upgrading some tests from NUnit 2.2.8 to 2.5.8 and noticed they were running a lot slower with the newer version of NUnit. I managed to narrow it down to their usage of log4net.

For example, the following test runs in 0.06 seconds on my machine using 2.2.8, but with 2.5.8 it takes 4.5 seconds. This is using .NET 2.0 on 32-bit Windows 7.

[Test]
public void Test1()
{
    log4net.ILog logger = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
    for (int i = 0; i < 3000; i++)
    {
        logger.ErrorFormat("test");
    }
}

See the attached VS2005 project for a complete example.

One workaround I found is to do the following in the constructor:

LogManager.GetRepository().Threshold = Level.Off;

This seems a bit strange, because there is no logging visible in either case, yet it runs much slower without that line. Is this expected behaviour?