I have experienced this problem with both 2.5 and 2.6.
When creating post and pages, on multiple sites I have had the same problem. When starting a new post or page and when adding custom fields, saving the content, editing the permalink WP creates duplicate or multiple drafts and instances.
For example, prior to writing this I wanted to create a page, so I started by editing the title, the parent page and add keywords field when I clicked save the page reloaded. There was a title and a new permalink, but no keywords or parent page. I edited the permalink and hit save again, then I went to manage pages to investigate. There were 3 new pages created with the same title with one of them under the actual parent page I selected when I first started.
When I create a new post, while I write WP autosaves. When I publish there is a duplicate posts of the same in the drafts.
What is going on. It is a pain having to clean up all of this and constantly checking the page and post setting to make sure they have everything correctly before they are published or if the correct version is being used.