map.entrySet().each { it.value = "foo" } should either update map or explode

def x = [a:1, b:2, c:3]
x.entrySet.each

println x

1. Prints [a:1, b:2, c:3] – would expect it to print [a:1, b:4, c:9], or to explode.
2. Instead of either updating or exploding, it silently fails.
3. Note: http://java.sun.com/j2se/1.5.0/docs/api/java/util/Map.html#entrySet() – the entrySet is explicitly backed by the map,
4. and by requirement of the Java API, changes to the entrySet must be reflected in the underlying map.