OverlapOnlyPawn Collision preset not working properly.

Hey guys! In third person game template I made a windmill actor with spinning blades. I made a sphere collision. If player trespasses the collision, then windmill’s blades stop. It works well but the collision is strange. I made an OverlapOnlyPawn preset and I don’t know why, but I still can climb the sphere collision. But there is the overlap event. So character is not walking on the collision, but it seems that he is kind of inside of this collision.
I kind of solved this problem by setting Visibility collision to Overlap instead of Block. So why does that Visibility collision mean and how to fix this problem?