All async unit tests timeout

Question

I am trying to run FlexUnit tests through Ant in a very simplified version of the sampleCLIProject. The tests pass when I compile through Flash Builder and timeout when I run them through Ant on Windows. This timeout problem only occurs in the case of async tests. When I run them through Ant on Mac OS X, Ant is unable to receive data back from Flash Player.

Here's the main application that runs the tests:

TestRunner.mxml

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
                xmlns:flexUnitUIRunner="http://www.adobe.com/2009/flexUnitUIRunner"
                layout="absolute"
                creationComplete="runTests();">
    <mx:Script>
        <![CDATA[
            import org.flexunit.demo.EchoPanelTest;
            import org.flexunit.listeners.CIListener;
            import org.flexunit.listeners.UIListener;
            import org.flexunit.runner.FlexUnitCore;

            public function runTests() : void {
                var core : FlexUnitCore = new FlexUnitCore();
                core.addListener(new UIListener(uiListener));
                core.addListener(new CIListener());

                core.run(EchoPanelTest);
            }
        ]]>
    </mx:Script>
    <flexUnitUIRunner:TestRunnerBase id="uiListener" width="100%" height="100%"/>
</mx:Application>

Here's the relevant part of Ant build file:

build.xml

    <target name="compile">
        <mxmlc file="${SRC_DIR}/TestRunner.mxml"
               output="${BIN_DIR}/Main.swf">
            <library-path dir="${LIB_DIR}"
                          append="true">
                <include name="*.swc" />
            </library-path>
            <compiler.verbose-stacktraces>true</compiler.verbose-stacktraces>
            <compiler.headless-server>true</compiler.headless-server>
        </mxmlc>
    </target>

    <target name="run"
            depends="compile">
        <chmod file="${BIN_DIR}/Main.swf"
               perm="777" />

        <flexunit swf="${BIN_DIR}/Main.swf"
                  timeout="5000"
                  toDir="${basedir}/reports"
                  haltonfailure="false"
                  verbose="true"
                  localTrusted="false"
                  command="${FLASH_PLAYER}" />
    </target>