Are you sure the Seller signed your offer with no changes whatsoever? If they signed it without making any changes, and the fax you are waiting for is merely your acknowledgment, then it's not likely someone can buy the house out from under you. I don't think Oregon is different from California in that regard. If your offer was truly accepted with no changes at all, then normally you would not have to worry about being bumped by a subsequent offer.... more
I agree with most previous posts. I too have represented buyer and seller in same transaction successfully. However, in the State of Wisconsin we have what is called designated agency. I'm not sure if Oregon has this or not and even if the term is different, it simply means that the broker could agree with the current agent to designate another agent in their office, and offer a referral fee to the first agent.
See if that is available to you.
Otherwise, as the others have said, this is not uncommon and can be done successfully.