I am a WordPress plugin developer and have developed plugins such as Wordpres Automatic Upgrade and Better Comments Manager.
My latest plugin uses WordPress XMLRPC and in that when i try to publish a draft post does XMLRPC does not set the correct date.
The method in question is wp_update_post wherein the date is set only by $post in the file post.php on line 734 and the $postarr date is ignored all together, this is because for drafts all post_date is set to 0000-00-00 00:00:00 and since the line in question sets the clear_date = true all $post_arr dates are cleared.
I have tried this with my own plugin and also windows live writer both are true while publishing drafts from the said softwares.
In both cases the publish date is set as 1999-11-30 12:00:00.