When multiple users play with similar data and one of the navigation property (to a list of children for example) has hard deletable items, it is possible for one user to load all the children in cache, then for another to delete those children. Then, for user 1, even if he refetches the parent objects with an expand clause to the children, Breeze will currently reattach even those children that were not returned from the server - the deleted ones. There is no easy way currently out of manually clearing the cache or querying directly for each child to check for deleted children. Since an Expand should always return all children, other children could be removed from cache.