Weird Problem with optional function parameter

I am having the most weirdest problem. I have an empty game object on which i attach a script name Test.cs

I can not have any function with optional parameter within Test.cs. If I do it gives me the following error on the component tab "The associated script cannot be loaded. Please fix any complie errors and assign a valid script". But note that there is no error on the console. More interesting thing is, I have been testing different things and I found out that as long as I am in a namespace it causes this issue. If I am not in a namespace, it doesn't.

The following code works

 using UnityEngine;
 using System.Collections;
 using Widgets;
 
 public class Test : MonoBehaviour{
 
     void foo(int index = 1)
     {
 
     }
 }

However this does not work as I add the namespace

 using UnityEngine;
 using System.Collections;
 using Widgets;
 
 namespace Widgets {
 public class Test : MonoBehaviour{
 
     void foo(int index = 1)
     {
 
     }
 }
 }

And the following works since I remove the optional function parameter

 using UnityEngine;
 using System.Collections;
 using Widgets;
 
 namespace Widgets {
 public class Test : MonoBehaviour{
 
     void foo(int index)
     {
 
     }
 }
 }

This bizarre problem is driving me crazy. Please help