CiviMail email attachments disappear if there is a form validation error

On step four of the CiviMail wizard there is a section for adding attachments to the emails. If you add an attachment and submit the form, but there is then a form validation error (ex. you forgot to fill in the subject field), your attachments will have disappeared. You'll need to re-add them to the form. And unless you have a keen eye you won't even notice.