A DESCRIPTION OF THE PROBLEM :
The fx:deploy ANT task does not always pass-on the value of its verbose attribute to the underlying javapackager implementation. I.e. class com.sun.javafx.tools.ant.DeployFXTask should always invoke
  deployParams.setVerbose(verbose);
in its execute method instead of only in one of its isModular branches.
As a result, no debug output is available and the temporary directory with all the configuration files is not retained. This makes debugging problems with building DMG bundles on macOS very, very difficult.

REGRESSION : Last worked in version 8u172

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the attached ANT build script on macOS 10.12.x with JDK 10.0.1.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Lots of debug output, temporary directory with configuration files is retained.
ACTUAL -
No debug output, temporary directory is deleted once the task finishes.

---------- BEGIN SOURCE ----------
<project
 name="test"
 default="all"
 xmlns:fx="javafx:com.sun.javafx.tools.ant">

  <target
   name="-init">
    <property
     name="tgt.dir"
     value="${basedir}/tgt"/>
    <property
     name="src.dir"
     value="${tgt.dir}/generated-sources"/>
    <property
     name="bin.dir"
     value="${tgt.dir}/classes"/>
  </target>

  <target
   name="-create"
   depends="-init">
    <mkdir dir="${src.dir}/test"/>
    <echo file="${src.dir}/test/Main.java">package test;

import java.awt.Dimension;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Main {
    private Main() {}

    public static void main( String[] args ) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Main().start();
            }
        });
    }

    void start() {
        JPanel contentPane = new JPanel();
        contentPane.setPreferredSize(new Dimension(480, 360));
        contentPane.add(new JLabel("Hello World!"));

        JFrame frame = new JFrame(getClass().getName());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(contentPane);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}
</echo>
  </target>

  <target
   name="-compile"
   depends="-create">
    <mkdir dir="${bin.dir}"/>
    <javac
     includeantruntime="false"
     destdir="${bin.dir}"
     srcdir="${src.dir}"/>
  </target>

  <target
   name="-bundle"
   depends="-compile">
    <jar
     basedir="${bin.dir}"
     destfile="${tgt.dir}/main.jar">
      <manifest>
        <attribute
         name="Main-Class"
         value="test.Main"/>
      </manifest>
    </jar>
  </target>

  <target
   name="all"
   depends="-bundle">
    <property
     name="java.lib.dir"
     value="${java.home}/lib"/>
    <property
     name="javafx.ant.lib"
     value="${java.lib.dir}/ant-javafx.jar"/>
    <available
     file="${javafx.ant.lib}"
     property="javafx.ant.lib.exists"/>
    <fail unless="javafx.ant.lib.exists">Could not locate JavaFX ANT tasks.</fail>

    <taskdef
     resource="com/sun/javafx/tools/ant/antlib.xml"
     uri="javafx:com.sun.javafx.tools.ant"
     classpath="${javafx.ant.lib}"/>

    <fx:deploy
     verbose="true"
     nativeBundles="dmg"
     outdir="${tgt.dir}"
     outfile="Main">
      <fx:application
       id="test.Main"
       version="0.1"
       name="Main"
       mainClass="test.Main"/>
      <fx:bundleArgument
       arg="mac.signing-key-user-name"
       value="DoNotSign"/>
      <fx:resources>
        <fx:fileset
         dir="${tgt.dir}">
          <include name="main.jar"/>
        </fx:fileset>
      </fx:resources>
    </fx:deploy>
  </target>

</project>
---------- END SOURCE ----------

FREQUENCY : always