Member A ignores Member B. Member A is subscribed to email updates to a thread. Member C quotes a post by member B. Member A receives an email alert showing the ignored content from Member B and the post from Member C.
Member A clicks through the to the thread from the email link and sees the post with the quote from Member B. On refresh the quote disappears and post disappears.
A member of my forum pointed out that ignored content is hidden via CSS. Which fine and dandy but there is no check for ignored content before an email alert is sent out therefore email alerts don't respect the ignore list.