From Jonathan Gibbons:

The line that is a problem is this one:
http://hg.openjdk.java.net/code-tools/jtharness/file/6c2635575044/src/com/sun/javatest/agent/SocketConnection.java#l226


           ServerSocket serverSocket = new ServerSocket(port, backlog);


The problem is that on Solaris, when port==0 and when using high concurrency, this code is subject to race in the underlying code, such that
another thread can "steal" the port that gets allocated.

The original background details are here:
https://java.se.oracle.com/infrabugs/browse/INFRA-12103
The jtreg aspects of this are here:
https://bugs.openjdk.java.net/browse/CODETOOLS-7902047
And the jtreg fix is here.
http://hg.openjdk.java.net/code-tools/jtreg/rev/986882b3be7e

The fix for JT Harness should be very similar, although you might want to may it conditional on port==0.