created_at of Sprint sometimes is null using API

Hello,
I am developing an application to import some of our Backlogs, Themes, etc into a Database for further reporting purposes.

But i'm running into troubles as the "created_at" attribute of some SprintStories contains "null" as you can see here:

{"created_at":null,"id":12083,"position":1,"sprint_id":3670,"sprint_story_status_id":4,"story_id":106162,"updated_at":"2012-06-26T14:07:43Z"},{"created_at":null,"id":11739,"position":4,"sprint_id":3670,"sprint_story_status_id":4,"story_id":59236,"updated_at":"2012-06-26T14:07:35Z"}

As the document does not state the attribute "created_at" to be nullable, I'm wondering whether this may be a bug?

Also there is a "bug" in the documentation of the Sprints (http://easybacklog.com/api#sprints).

In the list of available attributes on the left, you have listed "created_at" twice.

One of them should be named "completed_at" I think :)

Thanks for your help!

Best regards

Josef