Oncomplete does not get called after redirect

[rmartony]

I have the following problem:

In a page there's a button that after it is pressed should call the oncomplete javascript code.

<a4j:commandButton id="generatePDF"
 action="#{handler.generateResult}"
 value="Test PDF"
 oncomplete="alert('bla bla'); disableAllButtons();"
 reRender="msgs, checkboxes">

Also the generateResult method redirects to a servlet that displays a PDF document.

public String generarteResult() {
...

 FacesContext context = getFacesContext();
 context.getExternalContext().redirect("PDFViewServlet");

 return null;
}

The PDF document is displayed properly, but oncomplete is not called afterwards.
If I comment the redirect sentence, oncomplete gets called.

I am missing something?

I'm using:

JSF 1.2
Richfaces 3.2.1 GA
JBoss 4.2.2 GA

Any help would be appreciated.

Thanks,
Rafael..