Stored list is not immutable

I'm not sure if it's a bug, or if it is intended, but it's not working as I expected.

I would expect that all the objects in the Hive are immutable. Is this really a correct behavior, to be able to change the stored object without explicit Save in the Hive?

Scenario:
* I have a model that contains a list of numbers
* I store the model in the Hive
* I load the model from Hive, retrieved the list, and modify one element without saving it back to the Hive
* I load the model again, and the modified element in the list is there.

No file or test path is provided. Start by reproducing the reported Hive scenario with a Dart model containing a list: store it, load it, mutate one list element without saving, and load it again. Done means the intended behavior is established and the observed persistence of the unsaved mutation is either prevented or documented as expected.

Written by the indexing model from the issue text.