Release 1.30 all test results are duplicated

Since version 1.30 _(1.29 still works)_, all my tests are reported twice, duplicating all test results.
Probably caused by fix [JENKINS-48583](https://issues.jenkins-ci.org/browse/JENKINS-48583).

Each suite is reported once, all tests inside it are reported twice (once with the original name and once appended with '_2'; e.g. my.package.name.suite.testCaseOne and my.package.name.suite.testCaseOne_2).

Configured publish report 'fileset includes': **/report/test/TEST-*.xml

I'm also using the Parallel Test Executor plugin to run all my tests in parallel in 6 jobs running on different nodes.

If more information is required please let me know.

_Also posted this bug in [Jenkins buglist](https://issues.jenkins-ci.org/browse/JENKINS-63490)_ (not sure where to file this issue; was no response in Jenkins ticket).

Start by reproducing the report with the configured fileset **/report/test/TEST-*.xml and six parallel jobs on different nodes, comparing version 1.29 with 1.30. Investigate how the JUnit plugin combines results from parallel execution; done means each suite and test appears once, without duplicated names ending in '_2'.

Written by the indexing model from the issue text.