The website is being (slowly) updated with an eye towards maintainability and, eventually, performance. Part of this process means upgrades to various pieces of the underlying software. One of those components relates to email addresses. The system never permitted email addresses to be shared, although there were ways to circumvent that restriction. That is no longer the case. All the duplicate addresses have been removed. In most cases the true owner was obvious; in several, it was not. If you notice that your email address is missing and are unable to enter it, click the search button, select the 'users' tab, and enter the email address. The 'owner' will be listed. In all the cases of ambiguous ownership, the shared users were in the same council, so it shouldn't be difficult to rectify the situation.
Note: when new users are created (via membership management) an email address of email@example.com is created for each new user. This is recognized internally as a non-email address.