If the implicit collection should be referenced, XStream cannot build a valid reference:

    static class WithNamedList extends WithList {
        private final String name;

        public WithNamedList(final String name) {
            this.name = name;
        }
    }

    public void testReferenceByXPathWorksWithReferencedImplicitCollection() {
        xstream.alias("strings", WithNamedList.class);
        xstream.addImplicitCollection(WithNamedList.class, "things");
        WithNamedList[] wls = new WithNamedList[]{new WithNamedList("foo"), new WithNamedList("bar")};
        wls[0].things.add("Hello");
        wls[0].things.add("Daniel");
        wls[1].things = wls[0].things;
        String xml = xstream.toXml(wls);
        System.out.println(xml);
    }


<strings-array>
  <strings>
    <name>foo</name>
    <string>Hello</string>
    <string>Daniel</string>
  </strings>
  <strings>
    <name>bar</name> reference="../strings"
  </strings>
</strings-array>