I am a moderator of phpbbportugal forum and if I edit this post from an admin:
Since I don't have permissions to add attachments, after fix any error on the text and then submit. It will delete the attachment from the post, and the attachment was already there, sended by the admin.
I know I don't have permissions to add attachments, but since it was added by other user then me the user that is editing that post, it should send the post without losing the attachment, since it was added not by me.
Basically, phpbb should save who adds the attachments for each post, and if someone that is not the author edits that post and without having permission to add attachments, it should keep the attachment and not remove it from post...
We can see that on viewforum it still appears the icon of the existance of attachment:
But inside, we can't see nothing no more: