Weld-servlet 1.1.1-Final identifies tomcat 7 as tomcat 6 environment.In Listener.java it executes the following code

container = checkContainers(cc, dump, Arrays.asList(
Tomcat6Container.INSTANCE,
Tomcat7Container.INSTANCE,
Jetty6Container.INSTANCE,
Jetty7Container.INSTANCE,
JettyPost72Container.INSTANCE)
);

This method returns a Tomcat6Container as Tomcat 7.0.11 at least has the class org.apache.catalina.core.ApplicationContextFacade. I would suggest reversing the order to have Tomcat7Container checked first as I from my knowledge the class org.apache.tomcat.InstanceManager is new to Tomcat 7