Can't answer your question, but a London friend of mine called Maughold, 'Muffled' (bearing in mind a London 'U' is more of an 'A'), because of the augh in Ballaugh being aff. I have to add, he has his tongue in his cheek when he said this. However, I agree, it is confusing.

But then, you could apply this to the English language as well, couldn't you? - Susanne.