Our Sensei has been coming to class late for the past few weeks, for family reasons. A sempai (his 'oldest' student, actually) has been taking over and giving us classes on a regular basis. I called him 'Sensei' today and he got upset, and told me to call him 'Sempai'. But Sensei wasn't around and we had no idea wether he was going to show up today or not anyway.
Isn't it proper/ethical to call him Sensei, especially that he teaches Aikido himself (but at other dojos)?
I mean, when Sensei isn't around and might not show up, and a Sempai takes over, doesn't he automatically become a 'subtitute Sensei'? What do you think? Or better still, is there some sort of an ethical code relating to such cases?