Page is a not externally linkable
-- Google SEO News and Discussion
---- Combat a type of duplicate content by adding a blank hash mark "#"
Receptional_Andy - 10:24 pm on Oct 21, 2009 (gmt 0)Thread source:: http://www.webmasterworld.com/google/4009765.htm
Google have been making moves to encourage the # as a part of the URL to be processed by a server, rather than the client. What's you're seeing may be an unintended consequence of that, alongside AJAX - as you mention.
Brought to you by WebmasterWorld: http://www.webmasterworld.com