After Haku flies out of the bedroom we see Sen's left hand touching more of the blood on the railing. The elevator attendant sees it on the same hand
after grabbing her arm as she tries to board it. Not much later we see her looking at the same hand again before running across the pipe.
It isn't till after being held captive by the baby under the cushions that the blood switches hands as he holds her by the left arm revealing no blood on that hand at all.
The goof item below may give away important plot points.
When Haku has collapsed and turned back into his original form in the boiler room, he is seen clearly lying down with his head facing Kamaji's post. Then when Sen says her goodbyes to him for now, he is no longer pointing to Kamaji's Post. He is seen back facing his post when he wakes up.