surprise in Hadoop log

When I started working with Hadoop I was confused by next message in logs:

DEBUG conf.Configuration: java.io.IOException: config(config) 
    at org.apache.hadoop.conf.Configuration.<init>(Configuration.java:225) 
    at org.apache.hadoop.mapred.JobConf.<init>(JobConf.java:183) 

It was Hadoop 1.0.3 and I didn't understand "what am I doing wrong?". It was just the newest Hadoop and I didn't find more information in Google, So, I was need to check source code... surprise! Look at it (line 4!):

public Configuration(boolean loadDefaults) {
    this.loadDefaults = loadDefaults;
    if (LOG.isDebugEnabled()) {
      LOG.debug(StringUtils.stringifyException(new IOException("config()")));
    }
    synchronized(Configuration.class) {
      REGISTRY.put(this, null);
    }
    this.storeResource = false;
  }

I can't believe they always log exception... strange way to get stack trace? maybe...