EllisLab/CodeIgniter — pull request #1260 by Razican (2012-04-15 11:35:30+00:00)
Title: Added the ability to insert objects with insert_batch() in Active Record

We now can't pass an array of objects to that function, we can only pass an array of arrays or an object of arrays. With this fix, we can pass an array of objects or an object of objects to the insert_batch() method.

This is a post in the CI forum, where you can see the problem:
http://codeigniter.com/forums/viewthread/215142/