WordPress MU

Morning all,

I've been beating my head over this for the last few hours and cant find a solution.
I run a WPMU install for a Uni.
The situation is this.
I have two users who are admins of their own blogs.
Leonard owns blog 1
John owns blog 2.
How does Leonard add John as an editor of Blog 1 or vice versa?

If Leonard users the 'Add new' user function to add John, he gets a 'Sorry, that email is in use' error.

Now *I* can go into the core admin options and add the two together, but I shouldnt have to go in and edit a blog everytime an admin wants to add an existing user.

Thoughts, suggestions, comments, number for a preist? :P

The message should be a confirmation: "Invitation email sent to user. A confirmation link must be clicked for them to be added to your blog."

I have WPMU2.9.2 and just tried using normal users to add existing normal users in a variety of roles and it works as expected.

Do you have a place you can install 2nd instance of WPMU? Try there with a fresh download, if it works get all forensic with what your live install differences are(plugins etc).