After upgrading from 1.503 to LTS 1.509.4 and updating plugins to the latest released versions that work with LTS, I stopped getting JUnit test results in my build e-mails. I use a custom jelly script based on the html.jelly template (the JUnit section of my template is identical to html.jelly).

In my jenkins.log I see:
WARNING: Caught exception evaluating: it.JUnitTestResult. Reason: java.lang.reflect.InvocationTargetException
...
Caused by: java.lang.NoClassDefFoundError: hudson/maven/reporters/SurefireAggregatedReport
at hudson.plugins.emailext.plugins.content.ScriptContentBuildWrapper.getJUnitTestResult(ScriptContentBuildWrapper.java:78)
...

This seems like it might be related to https://issues.jenkins-ci.org/browse/JENKINS-16990, but I'm not sure how the fix for that issue applies in my situation.