Update comment.

test/unit/dom-if.html

@@ -962,9 +962,9 @@
       observer = el.shadowRoot.querySelector('#observer');
       // Note that path bindings in a falsey dom-if will be updated when the
       // dom-if becomes truthy, however path notifications to other elements
-      // will be lost; this is a fundamental limitation due to the fact that
-      // batched path notifications are not supported. Hence the `propChanged`
-      // count increments, but the `pathChanged` count does not.
+      // will be lost; this is a fundamental limitation (#4818) due to the fact
+      // that batched path notifications are not supported. Hence the
+      // `propChanged` count increments, but the `pathChanged` count does not.
       assert.equal(observer.propChanged.callCount, restamp ? 1 : 2);
       assert.equal(observer.pathChanged.callCount, 1);
       document.body.removeChild(el);