Emoticon Images From Mail Notification Are broken

When using Confluence 4.2.7 and 4.2.5 the notification mail images are broken.

I commented on a page using the ( y ) and ( n ) emoticons. In the notification email that was sent, the emoticons are shown as broken images.

I examined the HTML source of the notification email and saw that the emoticon images are referenced with relative paths which will not work from an email client: