Can't stop the bounce

I have a sphere, whose material has Bounciness=0 and Bounce Combine=minimum. The sphere is moving along a downward-sloped, bumpy, procedurally generated mesh. The mesh has a material with the same bounciness settings. The mesh's material is applied in code, and I've confirmed that it really has the material by looking in the inspector in play mode.

Despite this, the ball keeps bouncing. It rolls down a bit, and hits a bump, which launches it into the air. From then on, it repeatedly flies down the slope a bit, hits the ground, and bounces. The ball has a controller attached, but the behavior is the same when I comment out `FixedUpdate`.

I can force the ball to stay on the ground in code, but I'd rather do it with the physics engine, so that I don't have to completely disable the ability to be launched into the air.

If it helps, one other unexpected behavior is that the ball slides down the hill, rather than rolling. No axes are locked. Most of my experience to this point has been with 2D games, where circles roll at the slightest provocation.

 

I'll try one bump, then give up.