differences when compiling a project using flex builder and flex sdk

Question

The following code compiles fine in flex builder 3, but throws an error when compiled using the command line and flex sdk 3.3.

<?xml version="1.0" encoding="utf-8"?>
<ww:TestApplication
    xmlns:mx="http://www.adobe.com/2006/mxml"
    xmlns:ww="*"
    layout="absolute"
    backgroundColor="#FFFFFF"
    >
    <mx:Label x="10" y="10" text="simple test"/>
</ww:TestApplication>

The error message is: Unable to locate specified base class 'TestApplication' for component class 'TestApplication'.

The problem only happens when I use the default package for my custom classes. If instead I use

xmlns:ww="somepackage.*"

and change my matching AS class accordingly, then it compiles fine using the sdk. Am I missing an argument when compiling or something? Are there differences when compiling a project using flex builder and flex sdk? If so, which ones?