NavMesh is on dynamically created NavMeshObstacle and slips away

Hey there.

I got a navmesh attached to an npc which walks over the map.
At some time a NavMeshObstacle occurs at the current position of the npc.

The navmesh should detect he is not allowed to be on this place and should walk away (or maybe just stop moving). But instead he slips away to get out of the obstacle.

Whats the problem here? Is there a way to achieve this?
Even if I set navmeshagent.isStopped, he slips away.