There seems to be an issue that has become apparent with the move to ObjectIDs.

If we have a referenced association in our document and we set the association's id manually with a string, it gets persisted as a string. With the default behaviour of using ObjectIDs, I would expect it to cast the string as an ObjectID. Is that a correct assumption or should we be casting it manually before setting the association id?

If my assumption is correct would it be just a matter of running the setter through cast_ids! ? If so we can look at getting a patch written up.