Ah, the master branch is also affected. Example:

http://buildbot.python.org/all/builders/x86%20Gentoo%20Refleaks%203.x/builds/47/steps/test/logs/stdio

1:35:05 load avg: 4.64 [212/406] test_socketserver passed -- running: test_subprocess (370 sec)
beginning 6 repetitions
123456
Warning -- reap_children() reaped child process 4641
.Warning -- reap_children() reaped child process 4708
..Warning -- reap_children() reaped child process 4832
.Warning -- reap_children() reaped child process 4916
Warning -- reap_children() reaped child process 4921
..