I experienced a similar glitch. Aggroed the demon from the top of the stairs and retreated back through the archway. He followed me up and tried a jumping attack but actually got stuck in the ceiling. His feet were still visible, sticking through the ceiling, and I was able to damage him by shooting arrows at them. He just stood there taking damage until the 117th arrow finally killed him. I have to say, by the end he had pretty dark soles.