The "View change" link in an email provides a diff between the previous version and the current version. At the time the email is sent out, that link is valid. As soon as the page changes again, the link is inappropriate as it still diffs the previous version and the current version, rather than the version the email is about.

This is because the links are of the form:
http://example.com/pages/diffpages.action?pageId=671416524&originalId=703954960
rather than
http://example.com/pages/diffpagesbyversion.action?pageId=671416524&revisedVersion=5&originalVersion=6