This is what I have found so far:
Joomla enabled switching from http to https in 10.0.12.
SSL Switchover Support
Joomla! 1.0.13 has address a few lingering bugs in the HTTP/HTTPS switchover support reintroduced in Joomla! 1.0.12. SSL switchover support should now work fluidly with seemless transitions between encrypted and unecrypted pages.
http://www.joomla.org/content/view/3994/1/Joomla 1.5 RC3
The next version of Joomla has deeper support for SSL and is looking stable enough that we could build directly in it. This forum discusses security issues and might mean more to you than me!