java/net/httpclient/RequestBodyTest.java failed intermittently with AssertionError

This has been observed once on windows 7 in jdk 9 dev nightly.

----------messages:(3/129)----------
command: main RequestBodyTest
reason: User specified action: run main/othervm RequestBodyTest
elapsed time (seconds): 33.713
----------System.out:(60/2584)----------
HTTP server port = 51100
HTTPS server port = 51103
Proxy port = 51106
Running test_request_body_type string and response type string and sync=false
OK
Running test_request_body_type string and response type byteArray and sync=false
OK
Running test_request_body_type string and response type byteArrays and sync=false
OK
Running test_request_body_type string and response type InputStream and sync=false
OK
Running test_request_body_type string and response type file and sync=false
OK
Running test_request_body_type byteArray and response type string and sync=false
OK
Running test_request_body_type byteArray and response type byteArray and sync=false
OK
Running test_request_body_type byteArray and response type byteArrays and sync=false
OK
Running test_request_body_type byteArray and response type InputStream and sync=false
OK
Running test_request_body_type byteArray and response type file and sync=false
OK
Running test_request_body_type byteArrays and response type string and sync=false
OK
Running test_request_body_type byteArrays and response type byteArray and sync=false
OK
Running test_request_body_type byteArrays and response type byteArrays and sync=false
OK
Running test_request_body_type byteArrays and response type InputStream and sync=false
OK
Running test_request_body_type byteArrays and response type file and sync=false
OK
Running test_request_body_type InputStream and response type string and sync=false
OK
Running test_request_body_type InputStream and response type byteArray and sync=false
OK
Running test_request_body_type InputStream and response type byteArrays and sync=false
OK
Running test_request_body_type InputStream and response type InputStream and sync=false
OK
Running test_request_body_type InputStream and response type file and sync=false
OK
Running test_request_body_type file and response type string and sync=false
OK
Running test_request_body_type file and response type byteArray and sync=false
OK
Running test_request_body_type file and response type byteArrays and sync=false
OK
Running test_request_body_type file and response type InputStream and sync=false
OK
Running test_request_body_type file and response type file and sync=false
OK
Running test_request_body_type string and response type string and sync=true
OK
Running test_request_body_type string and response type byteArray and sync=true
OK
Running test_request_body_type string and response type byteArrays and sync=true
OK
Running test_request_body_type string and response type InputStream and sync=true
----------System.err:(6/357)----------
java.lang.AssertionError
at sun.net.httpserver.ServerImpl.responseCompleted(ServerImpl.java:805)
at sun.net.httpserver.ServerImpl$Dispatcher.handleEvent(ServerImpl.java:294)
at sun.net.httpserver.ServerImpl$Dispatcher.run(ServerImpl.java:353)
at java.lang.Thread.run(Thread.java:804)
STATUS:Failed.`main' threw exception: java.lang.AssertionError