Ok, let's see if I understand this. If so, I am having same problem as Webs.
I open my blog and go to 'new post'. I then right click bookmarkilet and 'Add to Favorites'.
I then go to the link that you posted. While on that page, I go to my bookmarklet favorite.
When I do this I get the admin log-in page.
In regards to the suggestion of turning off http cache, is this the setting under Administration/Global/Templates? If so I removed the 1800 setting and still get log-in page.