What is the test for a party to waive their right to a jury trial?

I respectfully dissent from Section III A of the majority's opinion holding that the defendants forfeited their right to a jury trial. I do not believe that Rules 38 and 39 of the Federal Rules of Civil Procedure contemplate that one party to the litigation shall have an exclusive continuing option to determine whether a trial shall be by court or jury merely because the other side vigorously contended at one point that a court trial was mandatory. In my opinion, far more is required before we can declare that a party has waived its right to a jury trial. To create an implied waiver from defendants' conduct here denigrates the principle that every reasonable presumption be indulged against the waiver of a right to trial by jury. Pradier v. Elespuru, 641 F.2d 808, 811 (9th Cir.1981).