Strange results when using Context Menu and Camera

I have a script that creates a mesh from each corner of the view fustrum at a given distance.

When the script is run by playing the scene, the mesh is generated as expected.

When the context menu is used while playing or not playing the scene, the mesh Y values are correct, but the X values appear to be half of what they should be.

Is there a difference when using Camera.main with Context Menu compared to play mode?

Edit 2:

To hopefully Clarify this issue, I am including a Debug.Log.

This is the Debug.Log for all 3 possible ways of calling the function Startup() and calculating each vertex position based on Camera.main .

Why am I getting different results for the same script? , the only difference being the way the function is called.

 START 
 UL (-0.8, 0.6, 1.0) : UR (0.8, 0.6, 1.0)
 LL (-0.8, -0.6, 1.0) : LR (0.8, -0.6, 1.0)

 Constructing Mesh from ContextMenu
 UL (-0.4, 0.6, 1.0) : UR (0.4, 0.6, 1.0)
 LL (-0.4, -0.6, 1.0) : LR (0.4, -0.6, 1.0)

 UPDATE - mouse-click 
 UL (-0.8, 0.6, 1.0) : UR (0.8, 0.6, 1.0)
 LL (-0.8, -0.6, 1.0) : LR (0.8, -0.6, 1.0)

SO ... hit play ... function called ... calculations are perfect.

Right-Click on the script and use context menu ... whoops all the calculations are giving the wrong results.

Call the function by an input in Update ... wow, the calculations are correct.

Spot the difference : the time the calculations were wrong, the same function was run using Context Menu.

This is the problem, I am looking for an answer as this is actually greatly affecting how I build my scenes. Thankyou.

The direct Debug values of Camera.main fieldofview and aspect, the results are :

 START 
 fieldOfView 60 : aspect 1.333333
 
 Constructing Mesh from ContextMenu
 fieldOfView 60 : aspect 0.5744382
 
 UPDATE - mouse-click 
 fieldOfView 60 : aspect 1.333333
 

Edit :

I have updated my question with pictures to demonstrate the problem. It is only when using Context Menu that the problem occurs. To me this can only be caused by how Unity sees Camera.main. I need to know why the camera FOV is off when using the context menu.

When the script runs by pressing play :

When the script runs by using Context Menu :

Here is my working script :

 #pragma strict
 @script RequireComponent(MeshFilter, MeshRenderer)
 
 #if UNITY_EDITOR
 @ContextMenu ("Construct Mesh")
 function ConstructQuad() 
 {
     Debug.Log("Constructing Mesh from ContextMenu");
     
     Startup();
 }
 #endif
 
 var theCamera : Camera;
 var cameraTransform : Transform;
 
 private var mesh : Mesh;
 
 private var uv : Vector2[];
 private var verts : Vector3[];
 private var tris : int[];
 private var normals : Vector3[];
 
 public var uvSize : Vector2 = Vector2.one;
 public var uvOffset : Vector2 = Vector2.zero;
 
 public var distance : float = 1.0;
 
 
 function Start() 
 {
     Startup();
 }
 
 function Update() 
 {
     
 }
 
 function Startup() 
 {
     if ( theCamera == null )
     {
         theCamera = Camera.mainCamera;
     }
     cameraTransform = theCamera.transform;
     
     if ( !mesh )
     {
         GetComponent(MeshFilter).mesh = mesh = new Mesh();
         mesh.name = "ScreenMesh";
     }
     
     Construct();
 }
 
 function Construct() 
 {
     mesh.Clear();
     
     verts = new Vector3[4];  
     
     // calculate verts based on camera FOV
     var pos : Vector3 = cameraTransform.position - transform.position;
     
     var halfFOV : float = ( theCamera.fieldOfView * 0.5 ) * Mathf.Deg2Rad;
     var aspect : float = theCamera.aspect;
     
     var height : float = distance * Mathf.Tan( halfFOV );
     var width : float = height * aspect;
     
     // UpperLeft
     verts[0] = pos - (cameraTransform.right * width);
     verts[0] += cameraTransform.up * height;
     verts[0] += cameraTransform.forward * distance;
     
     // UpperRight
     verts[1] = pos + (cameraTransform.right * width);
     verts[1] += cameraTransform.up * height;
     verts[1] += cameraTransform.forward * distance;
     
     // LowerLeft
     verts[2] = pos - (cameraTransform.right * width);
     verts[2] -= cameraTransform.up * height;
     verts[2] += cameraTransform.forward * distance;
     
     // LowerRight
     verts[3] = pos + (cameraTransform.right * width);
     verts[3] -= cameraTransform.up * height;
     verts[3] += cameraTransform.forward * distance;
     
     // ** usual mesh stuff from here onwards **
 }