In 3.0.6-RC1, the attachments counter at the front page of the ACP, doesn't increment anymore when adding an attachment to an already existing post. So, when you post a new topic, and add a attachment while writing your post, there is no problem. But, when you post the topic, and later on EDIT your post and then add the attachment, the counter doesn't increment.

This is resulting in some strange things like "-1" when deleting the post again. After some testing, I found out this issue got introduced in r9843. I didn't have enough time to find out where exactly the problem is, but I will try to do that later.