Terrain detail meshes not appearing?

Hi,

I'm trying to add detail meshes to my terrain, but they are not appearing. Even in the terrain's inspector, they have no icons. I created a simple prefab with my detail mesh and set that, also tried setting the detail mesh directly, both yield the same invisible result.

However, I can manually place instances of this prefab in the scene. (And they are visible, of course)

Does anyone know what can cause functional meshes not to appear as detail meshes?

Also, in this tutorial it is stated that detail meshes don't have collision. If I add a prefab that contains a collider in it, it won't collide? (cant test yet because of first problem)