Threads not garbage collected ?

[Alex via Digitalmars-d]

import core.thread;

class A
{
        Thread mThread;
        bool mStopped;
        
        this()
        {
                mThread = new Thread(&run);
                mThread.start();
        }
        
        void run()
        {
                while (!mStopped)
                {
                        //do stuff
                }
        }
        ~this()
        {
                mStopped = true;
                mThread.join();
        }
}


void main()
{
        auto a = new A;
        delete a;               //need this or the program hangs
}

In both gdc and dmd I need to use manually delete this object or 
the program is blocked after main. Is by design ?
It seems undesirable, as the thread can be many layers of 
encapsulation down, and they all need manual deletes.