I have this test failing consistently with jdk9 b141 on macOS 10.12 and OS X 10.10.
As I understand, it should not seek the steam playing but it does: now, I'm not sure if it is a product issue.

[mts.java.AbstractTest] initialize test
url
[mts.java.AbstractTest] run test
onPlaying
time: 22353.552842999998 ms
attempting to seek
new time: 11100.144444444444
exp time: 24353.552842999998
[mts.java.AbstractTest] cleanup test
[mts.java.AbstractTest] test failed (expected = 24353.552842999998, actual = 11100.144444444444, precision = 500.0)
result: Failed. exit code 1

Note that the test does pass on Windows 10.

RULE "FXMediaTestSuite/mts/java/automated/HLSSeekDisabledTest/HLSSeekDisabledTest" ExitCode 1