The problem is that there is a registered bean (coming from JSF impl) of type com.sun.faces.context.RequestMap which is just a little more fancier Map.

One of the elements of this map (stored under key "org.jboss.weld.context.http.HttpRequestContext#com.sun.faces.cdi.RequestMapProducer" is the Map itself.
This OFC blows up when you try to do Map.toString() which is what using the EL expression ultimately does.

Now we "just" need to figure out whos is populating this map with itself...