Hi,
I am using Attachments 1.6.2.1 with WP3.4.1. When i am selecting the image it is displaying the default thumb from wp-includes folder. And after updating the post it is displaying correct image.
Please see the below screenshots:
http://awesomescreenshot.com/0a4bj9045 (before update)
http://awesomescreenshot.com/0a6bj9d7f (after update)