Unable to assign to user defined Object properties using id of existing object

Creating an object (in its own .qml file) whose purpose is to be used as a grouped property elsewhere (Obj1.qml in attached code) , create a second object which uses the grouped property "property Obj1 myObject1". When instances of the second object are created you can specify the myObject1 property by creating an instance of Obj1 on the same line e.g. :

myObject1: Obj1 {}

but not by referring to the id of an existing Obj1 Reference.

Obj1

.
.
.
myObject1 : myObj

as this gives at runtime :

Unable to assign QObject* to Obj1_QMLTYPE_0*