When a key is deleted the watched update doesn't fall back to inherited values

To reproduce:
1. Set a config to inherit
2. Set a key in the parent config
3. Verify the key in the child config
4. Set the key in the child config
5. Verify the key change in the child config
6. Delete the key from the child config
7. Any configuration which is watching for changes now will be missing the key, rather than using the parent key's value
