ThemeLoader and folder convention

Hello everybody,
In my application I use a custom ThemeLoader and ClientBundle. In the client bundle I have the annotation

@Source("styles.css")

in order to load my custom theme. I'd now like to place my theme under /WebContent/VAADIN/themes/myTheme, but if I try to place it outside of the widgetset descriptor file package (e.g. its parent) I get this warning at compile time:

[WARN] Resource 'com/example/[...]/styles.css' was located via ClassLoader. As a result changes in that resource will not be reflected in per-file recompiles. It should be registered via  <source /> or <resource /> entry in your .gwt.xml. In a future version of GWT, we will remove this fallback and your application will stop compiling

I tried setting the containing folder in the descriptor (both <source path=".." /> and <resource path=".." />) but the warning still appears.

Does anyone know what's the right way to do it?