FULL PRODUCT VERSION :
java version "1.8.0_161"
Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.161-b12, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Linux 4.13.0-37-generic (amd64)

A DESCRIPTION OF THE PROBLEM :
The test java/awt/dnd/URIListBetweenJVMsTest/URIListBetweenJVMsTest.html intermittently fails with the message "WARNING: Child process error stream is not empty!"
The issue was observed on Ubuntu 17.10
The reproducibility ~20%

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
failed=0
count=0
while [ ${failed} -eq 0 ]
do
  jtreg -ignore:quiet -v -a -xml \
      -exclude:exclude.tests \
      -testjdk:"$TESTJDK" \
      -javaoptions:"-Djava.awt.headless=false" \
      -timeoutFactor:2 java/awt/dnd/URIListBetweenJVMsTest/URIListBetweenJVMsTest.html
  failed=$?
  count=$((count+1))
  echo "${count}. failed=${failed}"
done

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
the test passes, no exceptions are expected
ACTUAL -
java.lang.RuntimeException: WARNING: Child process error stream is not empty

ERROR MESSAGES/STACK TRACES THAT OCCUR :
#section:applet
----------messages:(3/153)----------
command: applet URIListBetweenJVMsTest.html
reason: User specified action: run applet/othervm URIListBetweenJVMsTest.html
elapsed time (seconds): 9.428
----------System.out:(1/31)----------
Toolkit = sun.awt.X11.XToolkit
----------System.err:(18/1101)----------
========= Child VM System.err ========
Apr 06, 2018 4:35:21 PM sun.awt.X11.XToolkit processException
WARNING: Exception on Toolkit thread
java.lang.NullPointerException
at sun.awt.X11.XDropTargetEventProcessor.doProcessEvent(XDropTargetEventProcessor.java:48)
at sun.awt.X11.XDropTargetEventProcessor.processEvent(XDropTargetEventProcessor.java:119)
at sun.awt.X11.XToolkit.run(XToolkit.java:580)
at sun.awt.X11.XToolkit.run(XToolkit.java:532)
at java.lang.Thread.run(Thread.java:748)

======================================
java.lang.RuntimeException: WARNING: Child process error stream is not empty!
at test.java.awt.regtesthelpers.process.ProcessResults.verifyStdErr(ProcessResults.java:93)
at URIListBetweenJVMsTest.verifyTestResults(URIListBetweenJVMsTest.java:96)
at URIListBetweenJVMsTest.start(URIListBetweenJVMsTest.java:84)
at com.sun.javatest.regtest.agent.AppletWrapper$AppletRunnable.run(AppletWrapper.java:158)
at java.lang.Thread.run(Thread.java:748)
STATUS:Failed.Applet thread threw exception: java.lang.RuntimeException: WARNING: Child process error stream is not empty!


REPRODUCIBILITY :
This bug can be reproduced occasionally.

---------- BEGIN SOURCE ----------
http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/file/f940e7a48b72/test/java/awt/dnd/URIListBetweenJVMsTest/URIListBetweenJVMsTest.html
---------- END SOURCE ----------