Inheriting from an interface twice

[Denis Koroskin]

I always thought that in D interface inheritance is always virtual, i.e.  
you only inherit it once even if it is specified twice (or more) within  
hierarchy.

Until I got an assertion on the following test (reduced from a real  
example):

interface Foo
{
}

class Bar : Foo
{
}

class Baz : Bar, Foo
{
}

void main()
{
        Baz baz = new Baz();
        Bar bar = baz;
        
        Foo foo1 = bar;
        Foo foo2 = baz;
        
        assert(foo1 is foo2);
}


foo1 and foo2 have the same type and point to the same object. Yet they  
have different addresses. Is it a bug, or a feature?

The test above passes for C# (http://ideone.com/xK5Mu) and C++  
(http://ideone.com/MnnL8 virtual inheritance used, fails otherwise, of  
course).