Using WP4.3.1 and CIviCRM 4.6.9 I also had this happen on the current CiviCRM.org demo site for WP.
When editing a membership Civi sends receipt and confirmation even when the box for "Send Confirmation and Receipt?" is Unchecked.
Is this a bug or am I missing something? Of course we do NOT want to send receipts for most edits we make!