I had to move my blog off Tumblr shortly after moving on when I realized I couldn't access the archive when logged out. There's no way to turn this off. And as far as I can tell, there's no way to convince it you're logged in when viewing under a domain. I was logged in, but it still showed a logged out view. Something to do with cookies, I'm sure, but this was with default security settings. I'm sure I could fix it for me, but I can't expect everyone who visits to do that.
I moved (or will be) it to wordpress.com, so it's not like I don't trust you to host my blog. It's mainly about the change itself. The locking down of archives was an announced change on the Tumblr blog, so not a bug, and that would have been a deal breaker even if it worked for me.
