This happens with the plugin:https://wiki.jenkins-ci.org/display/JENKINS/Discard+Old+Build+plugin

When we execute two jobs at the same time, for example job #42 and #43, and the second one get's aborted, it won't remove the latest successful build because the job #42 is still in progress.
~~~ 13:58:41 #42 is still in progress; ignoring for purposes of comparison

Now when job #42 ends, it will remove itself leading to an empty directory.

The job #42 still exists, but opening the job/consoleLog shows:
~~~ No such file: /home/cosmin/Projects/Mozilla/mozmill-ci/jenkins-master/jobs/mozilla-central_remote/builds/2014-09-22_14-40-19/log