Thanks for this post and I'm so glad you escaped with your skin intact! 25 years ago we came close to disaster on a fully loaded tandem with cantilever brakes and aluminum rims. Did a big descent in the pouring rain and figured the rain would keep the rims cool. Looking at the bike in the sunshine the next morning we realized that the tire sidewalls were melted and frayed and we couldn't believe they had held together.
Tandems by nature are putting twice as much heat into the braking system than your typical user so we'll always be an edge case for the designers.
Be careful everyone.