I had a 79 Husqvarna 390CR which I rode in the desert. The drum brakes were barely adequate unless you encountered anything "wetter than a sneeze" according to a magazine review. If I rode through water and tried to stop I got that feeling that the bike accelerated when I squeezed the front brake. It's a weird feeling, your brain is expecting some slowing and when none occurs, it feels like you are speeding up.

I've had a similar feeling on road bicycles in the rain. When I rode mountain bikes in the snow with cantis, the snow builds up on top of the brakes so even if you brake hard enough to create heat, which would normally dry the pads, the melting snow keeps them wet. Throw some sand into the snow and rims don't last very long.