Rayhit normal is not fully normalized. It's seems that it lacks of precision.

1. Open project attached by Lukas.
2. Open scene "scene".
3. Play scene.
4. Select gameObject "Cube".
1. Set rotation.y to 90 degrees.
5. You should get log message saying that "hit= True, rayHit.normal= (0.0, 1.0, 0.0), Mathf.Acos(rayHit.normal.y)=NaN
UnityEngine.Debug:Log(Object)
RaycastBehaviour:Update() (at Assets/RaycastBehaviour.cs:18)". It means rayHit.normal.y is higher then 1.

Workaround: normalize rayHit normal.

Regression: 4*
Reproduced: 5.0.0f2, 5.0.0f1, 5.0.0b15