just to reiterate here: when you change node properties in the topic tree, they will be reflected in the node cache.  If you add/remove nodes entirely, then the node cache won't have slug keys pointing to the new nodes (or will have slug keys pointing to old, removed nodes).  

So in that case, easiest thing to do is to run `get_node_cache(force=True)`, which will walk through the through the topic tree to rebuild the `node_cache` from scratch.