in src/main/java/org/apache/sling/jcr/base/internal/mount/ProxySession.java [588:600]
public Node addNode(String parent, String path, String name) throws RepositoryException {
if (isMount(path)) {
return wrap(this.mount.getNode(parent).addNode(name));
}
if (isMountParent(path)) {
this.mount.getNode(parent).addNode(name);
if (sync == null) {
sync = new HashSet<>();
}
sync.add(path);
}
return wrap(this.jcr.getNode(parent).addNode(name));
}