The following code produces the error:  "Error: class Implementation ambiguous virtual function getNext"

interface Interface
{
	Interface getNext();
	const(Interface) getNext() const;
}

class Implementation : Interface
{
	Implementation getNext()
	{
		return null;
	}

	const(Implementation) getNext() const
	{
		return null;
	}
}

The error does not appear if "Interface" is changed to an abstract class.