If you set "embedded_object_id: false" in the mongoid.yml file; Then editing of embedded documents via a nested form doesn't save the new data when doing update_attributes. (Behaviour is not exhibited on embedded documents with an _id)

(This was found using the bb3e1390e313b4154964 commit from 2011-03-04) and rails 3.0.5)
Gist below:
https://gist.github.com/856934