A bank who obtained a payoff from the line of credit lender, paid off the loan, and filed a deed of trust. After the bank paid off the prior lender, the borrowers continued to draw on the line of credit loan from the prior lender. The Court of Appeals held that the refinancing bank had means of discovering that the payoff alone was insufficient to release the deed of trust and the prior lender was not estopped by virtue of having provided the payoff letter. The line of credit deed of trust conditioned the prior lender's release of the deed of trust upon the borrower requesting cancellation of the line of credit. Washington Mutual Bank, F.A. v. ORNL Federal Credit Union, Case No. E2007-02421-COA-R3-CV, ED Tenn. App. 2008)