extern(C) declaration inside function

[Luís.Marques]

When you declare an extern(C) function inside a D function it 
seems to continue to use D's name mangling, which is unexpected 
for me. For instance:

    void main()
    {
        extern(C) void foo(int);
        foo(42);
    }
    Undefined symbols for architecture x86_64:
      "__D4test4mainFZv3fooUiZv", referenced from:
            __Dmain in test.o

Is this a bug?