When setting expectations on an existing stub, block to evaluate responses is not executed

Hi,

this works (block is executed):
   
    http_request(:get, "http://www.example.com/")
    assert_requested(:get, "http://www.example.com/", :times => 1) { |req|
        # evaluate req
    }

but this does not (block is not executed):

    stub = stub_request(:get, "http://www.example.com/")
    http_request(:get, "http://www.example.com/")
    assert_requested(stub, :times => 1) { |req|
       # evaluate req
    }

I would expect the second example to work just like the first one.