C# Console Output Labeled in Build Log as [Test Error Output]

Console output from C# is intermittently labeled in the build log as [Test Error Output] which makes a mess of the log.  There appears to be no reason why some of the lines are labeled this way and some are not.  I am using C# and NUnit.  This is a very simple issue.  The console output statements are something like this:

Console.WriteLine("Creating Data");
Console.Write("Pausing...");


Update:
I think this is only happening when I have the build log open while the build is running.  If I refresh the build log then the previous [Test Error Output] messages disappear, but more more will show up as the log is written to.  I find this very odd, and it would be nice if someone can shed some light on why this happens.  Thanks.

Message was edited by: Cassius Mead