In the configuration view the "Retain long standard output/error" checkbox is always unchecked no matter what value the keepLongStdio element in the xml configuration file of the job has.
This is very annoying because when saving the configuration the value of the keepLongStdio xml element is set back to false if you do not reselect the checkbox.

The bugs has been probably introduced with changeset 31016 (see also bug JENKINS-6516).