If you load an item from the server with partial server-side included information, then load it a second time with additional information, relationships will not be correctly injected and updated on the item.

Example showing issue:http://plnkr.co/edit/YpLgDBxL1ro05MKR3v9h

Notice, when you first load the page, the single injectedParent.children item is picked up. Upon clicking the button, you would expect the list of children to update, but they do not. This is because_injectRelations is not called if the item already exists in the cache.

The issues caused by this extendmuch further than just the items not being in the cache. The child items are actually no longer DS resources (even if they were previously), and so they are missing all functions and other behavior that would be expected.