question

This seems like something we could improve. I'll add an issue to the dev list about it.

As a workaround, you can change the OnSet code of the parameter to add the new objects:

treenode reference = param(1);
Variant newValue = param(2);
Variant oldValue = param(3);
int isReset = param(4);

{ // ************* PickOption Start ************* //
/***popup:ParamSetNodeValue*/
/**Delete and Copy Group Members*/
if (/***tag:condition*//**/isReset/**/) {
    Array objects = reference.as(Group).toFlatArray();
    
    if (objects.length == 0) {
        mpt("Error setting parameter " + c.up.up.name + " - Not enough objects in object set"); mpr();
    } else {
        for (int i = 2; i <= objects.length; i++) {
            objects[i].destroy();
        }
        
        treenode firstObj = objects[1];
        int total = Math.max(1, newValue);
        for (int i = 2; i <= total; i++) {
            treenode newObj = createcopy(firstObj, firstObj.up);
            newObj.name = firstObj.name + "_" + i;
            applicationcommand("recreateObjectConnections", newObj, firstObj);
            
            treenode oldStored = stored(firstObj);
            treenode newStored = stored(newObj);
            for (int i = 1; i <= content(oldStored); i++) {
                treenode linkedObj = rank(oldStored, i).find("+/~");
                if (linkedObj && isclasstype(linkedObj, "StatisticObject") && !isclasstype(linkedObj, "GenericChart")) {
                    function_s(linkedObj, "addMember", newObj);
                }
            }
        }
    }
}

} // ******* PickOption End ******* //

Most of the code is the same. The new code is found beneath the call the "recreateObjectConnections". The basic idea is to check the stored node of the original object, and if it's linked to a Statistics Object that isn't a Generic Chart, then call its addMember function, adding the new object.