Questions come up some times about why things get bad data. It is hard to pin things down, as maybe you can't modify the code, or even know where to look. Here's an example of how to track down what's making bad trace ids in finagle.
$ (cd /tmp; wget -q http://downloads.jboss.org/byteman/3.0.5/byteman-download-3.0.5-bin.zip; unzip byteman-download-3.0.5-bin.zip)
$ export BYTEMAN_HOME=/tmp/byteman-download-3.0.5/