Mesh dissapearing from Resources

Essentially in runtime I'm loading a mesh from an object in "resources" and attaching it to an onscreen object. I am doing this like so:

 var o : GameObject = GameObject.Find("MyObject");
 var u : GameObject = Resources.Load("ResourcesObject");
 o.GetComponent(MeshFilter).mesh = u.GetComponent(MeshFilter).mesh;

Now this all works fine during runtime, the mesh is added to object "o" from object "u" however when I stop the program then the mesh on the object in resources (u) becomes missing. It is not like this during runtime even after it has been copied to "o", does anyone know why this happens and how I can stop it happening?

Thanks in advance!