> When I moved to the UK though, I was initially pretty "stand my ground" about only communicating in my accent -- after all, I was speaking perfectly correct English.

That's an interesting cultural difference. Here in France (at least around me) teachers insist on trying to develop an accent similar to a native English accent. From what I've read in this thread, I think they're trying to teach people Received Pronunciation. Having perfect English with still a noticeable French accent is generally looked down upon.