Spurious "does not override any function" when the inherited interface has errors

[VPanteleev-S7]

interface IFoo
{
	void foo();
	UnknownType bar();
}

abstract class Foo : IFoo
{
	override void foo() {}
}

Compiler output:

test.d(4): Error: undefined identifier `UnknownType`
test.d(9): Error: function `test.Foo.foo` does not override any function

The error on line 9 is spurious. The Foo class is perfectly fine, the problem is contained entirely in IFoo.