In Web Start for J2SE 1.4 (I believe) a feature was added that defined a collection of 'safe' properties that should be set at VM launch time. However, this only happens if one of those 'safe' properties is defined in the first <resources> element in the JNLP file.

This is particularly problematic on Mac OS X, since we tell developers that properties that are only relevant for Mac OS X should go into a resources element with the 'os="Mac OS X"' modifier, and common practice says that you should put the common properties and JAR files first in a platform-independent resources element, and then any OS/architecture/locale-specific elements after that.

Example of JNLP code that fails to set brushed metal property:
<resources>
  <! Platform independent resources -->
<jar href="myapplication.jar"/>
</resources>

<resources os="Mac OS X">
  <property name="apple.awt.brushMetalLook" value="true"/>
</resources>

Section 4.2 of the JNLP spec says that "[p]roperties set in the JNLP file may be set by the JNLP Client at any time before the application's code is executed; thus, it cannot be assumed that they will be set during the initialization of the virtual machine." Given that escape clause, this is technically correct behavior, but I think it's worth clarifying the current behavior of the code either in the JNLP specification, or at least documenting this restriction.