The fix for JDK-8223463 changed the test to use the loopback address. But the test will fail if the loopback is an IPv6 address because the the server does not support EPSV.
Both sun/net/ftp/FtpURL.java and sun/net/ftp/FtpURLConnectionLeak.java should also explicitly require NO_PROXY - it seems that on some configuration only 127.0.0.1 is configured as a no proxy host - and [0:0:0:0:0:0:0:1] goes through the proxy. This can make the test fail on Mac OS where the stack uses the system proxy by default.