[Hayet Maamouri]

Probably I, myself learnt the word from TV.
To answer your question, "Why do I have to teach RP?" simply because when I was a student myself I was taught RP and during my training we were asked to do that. Anyway I guess RP would always be a clear and safe way to communicate with others in English. I doubt that I still pronounce plenty of words the way I learnt them, that's due to TV influence and the fact that I no more seeing english people as when I used to when i still studied, 7 years ago. We had some foreign teachers with whom we enjoyed talking.
i'll have to ask about the reasons the next time i'll meet our inspector. by the way is the school year nearly over where you teach? here school will be over by the end of June.