JNLP -- Stack/Memory Size

Running on Snow Leopard (10.6.1). Java Prefs are set to use Java SE 6 (64-bit) first, both for applets and applications.

When I launch the following JNLP file, neither stack size or heap size is set properly. I can fiddle with the j2se element to get heap size set properly (using initial-heap-size="512m" and max-heap-size="1024m") but I can't set stack size. Sun's reference docs claim that -Xmx, -Xms, and -Xss should all be supported. Are they no longer supported in Apple's Java? Known bug or conscious decision?

JNLP file follows:

<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.5+" codebase="http://download.rptools.net/">
<information>
<title>RPTools MapTool</title>
<vendor> http://download.rptools.net/</vendor>
<icon href="http://www.rptools.net/images/logo/RPTools Map_Logo403.png"/>
<offline-allowed/>
<shortcut online="false">
<desktop />
<menu submenu="RPTools" />
</shortcut>
</information>

<security>
<all-permissions />
</security>

<resources>
<j2se version="1.5+" java-vm-args="-Xmx1024m -Xms512m -Xss8m"/>
<jar href="lib.php/maptool-1.3.b57.jar" />
<jar href="lib.php/BareBonesBrowserLaunch.jar" />
<jar href="lib.php/abeille-formsrt-2.0.jar" />
<jar href="lib.php/antlr-2.7.6.jar" />
<jar href="lib.php/clientserver-1.0.b14.jar" />
<jar href="lib.php/commons-beanutils-1.8.0.jar" />
<jar href="lib.php/commons-collections-3.2.1.jar" />
<jar href="lib.php/commons-jxpath-1.1.jar" />
<jar href="lib.php/commons-lang-2.4.jar" />
<jar href="lib.php/commons-logging-1.1.1.jar" />
<jar href="lib.php/decktool-1.0.b1.jar" />
<jar href="lib.php/dicelib-1.0.b18.jar" />
<jar href="lib.php/ezmorph-1.0.5.jar" />
<jar href="lib.php/hessian-3.1.6.jar" />
<jar href="lib.php/jide-common-2.4.8.jar" />
<jar href="lib.php/jide-components-2.4.8.jar" />
<jar href="lib.php/jide-dialogs-2.4.8.jar" />
<jar href="lib.php/jide-dock-2.4.8.jar" />
<jar href="lib.php/jide-editor-2.4.8.jar" />
<jar href="lib.php/jide-grids-2.4.8.jar" />
<jar href="lib.php/jide-oss-2.4.8.jar" />
<jar href="lib.php/jide-properties-2.4.8.jar" />
<jar href="lib.php/jl1.0.jar" />
<jar href="lib.php/js-1.7R1.jar" />
<jar href="lib.php/json-lib-2.2.2-jdk15.jar" />
<jar href="lib.php/log4j-1.2.15.jar" />
<jar href="lib.php/maptool.resource-1.0.b18.jar" />
<jar href="lib.php/parser-1.1.b20.jar" />
<jar href="lib.php/renderpack-1.2004.jar" />
<jar href="lib.php/rplib-1.0.b118.jar" />
<jar href="lib.php/sbbi-upnplib-1.0.4.jar" />
<jar href="lib.php/servicediscoverylib-1.0.b5.jar" />
<jar href="lib.php/swing-worker-0.1.jar" />
<jar href="lib.php/tinylaf-1.3.04.jar" />
<jar href="lib.php/withay-util.jar" />
<jar href="lib.php/xpp3_min-1.1.3.4.O.jar" />
<jar href="lib.php/xstream-1.2.2.jar" />
<jar href="lib.php/yasb-0.2-21012007.jar" />
</resources>
<application-desc main-class="net.rptools.maptool.client.LaunchInstructions">
<argument>run</argument>
</application-desc>
</jnlp>