Generated meshcollider is not working?

I have a game object with a mesh filter and a mesh renderer.

I use this code to add a mesh collider to the object:

 meshGameObject.transform.gameObject.AddComponent<MeshCollider>();
 MeshFilter modelFilter = (MeshFilter)meshGameObject.GetComponent("MeshFilter");
 meshGameObject.transform.GetComponent<MeshCollider>().sharedMesh = modelFilter.mesh;

This works. A mesh collider is added to the game object and it gets the mesh from the mesh filter.

My problem here is, that the mesh collider only works, when I disable and enable the mesh collider in the inspector. Else, it doesn't work.

Why? Is there something refresh for generated mesh collider?