WP3.1-RC4 & filter query (with meta key) not working

Hey, i’ve made a plugin to allow visitors to post from the frontend.
The posts are saved with a particular user which is the “guest” account; and when the visitor writes a post, he has to fill his name & email (custom fields).

The problem was that when displaying the posts from the “guest” account; all posts were listed and not only the posts by this particular visitor.
So I added a filter on queries (when doing an author query); which checks the email meta key if the author queried is the “guest” one.

When printing the query_vars of my query, I have
[meta_key] => oqp_guest_email
[meta_value] => [email protected]
which is what I want.
So only the posts which have that meta key and value should be returned.

But It does not work; it returns all posts from the “guest” acount.

I think it WAS working before I did the upgrade.
Any idea ?
Here’s the full code & explanations :
https://pastie.org/1579364

Thanks a lot !