I noticed the problem when i put seam-solder in my ear/lib folder.
Then if i mark my servlet as asynchrone in web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
<display-name>Mpulse test Servlet 3.0</display-name>

<servlet>
<servlet-name>MyServlet</servlet-name>
<servlet-class>eu.mpulse.test.MyServlet</servlet-class>
<async-supported>true</async-supported>
</servlet>

<servlet-mapping>
<servlet-name>MyServlet</servlet-name>
<url-pattern>/servletgrrr/hello</url-pattern>
</servlet-mapping>
</web-app>

a call to startAsync on the servlet throws:
"java.lang.IllegalStateException: The servlet or filters that are being used by this request do not support async operation"