Why implicitly call of the inner class instance not allowed? [duplicate]

I use groovy 2.4.18

A parent and inner child classes:

class Parent {
    def name
    def child = new Child()
    def call() {
        println('parent called')
    }
    class Child {
        def call() {
            println('child called')
        }
    }
}

Calling:

import base.Parent

parent = new Parent(name: 'parent')
parent()
parent.child.call()
parent.child()

output:

parent called
child called
Caught: groovy.lang.MissingMethodException: No signature of method: base.Parent.child() is applicable for argument types: () values: []
Possible solutions: call(), find(), find(groovy.lang.Closure), getChild(), setChild(java.lang.Object), split(groovy.lang.Closure)

This should be a bug. I am not 100% as we may have redefined when automatic expansion to call is valid (assigning child to a local variable x and then doing x() will work for example), but I would still suggest to enter an issue for this in the Apache Groovy JIRA.