Remove all friction from a supposedly frictionless wall

It's been asked before, but I still haven't found an answer.

I have a capsule character who is touching a wall (a primitive cube) and moving parallel to it by way of physics forces. The wall has zero static friction, zero dynamic friction, and its combined friction is set to minimum.

Yet... the capsule is slowed down as it moves along the wall.

Why is there still friction and how can I vanquish it once and for all?