immutable / inout / pure headaches

[Timoses]

I dared once again getting into immutable by adding an 
"immutable" keyword which causes a chain of actions to be taken.
I feel like I'm lost in a jungle of immutable, inout and pure 
(perhaps more will join the party...).

To start off, why does this not work?


	class Test
	{
		private S s;
		this(S t) { this.s = t; }
		this(immutable S t) immutable { this.s = t; }

         inout(Test) get() inout
         {
             // Error: none of the overloads of __ctor are 
callable using a inout object, candidates are:
//onlineapp.d(10):        onlineapp.Test.this(S t)
//onlineapp.d(11):        onlineapp.Test.this(immutable(S) t)
          	return new inout Test(this.s);
         }
	}

	struct S
	{
		int[] a;
	}
	void main()
	{
		immutable S s = immutable S([1,2,3]);
		auto t = new immutable Test(s);
	}