It is always out of courtesy that the proper names should be pronounced as in their original languages. But as far as I'm concerned (maybe it's prejudicial to think this way-I hope our AE speakers reply) Americans mostly do it the other way round.
I've heard that too - 'i' and 'e' seem to be more-or-less interchangeable in the English pronunciation of anything Latinate: last month I was singing in a choir in which the entire soprano section insisted on singing In dulcE jubilo (in spite of the fact that the words In dulci jubilo actually mean something different :-()