That's an interesting anecdote about near-perfect mastery having downsides! I can provide a different one but on the same theme. I saw a documentary a while back in which an immigrant sadly explained that if she made her absolute best effort to adapt and speak Swedish, she would get really crappy service in stores and such because of her accent and grammatical errors. If, instead, she spoke English (which she commanded better) she would get excellent service from everyone who were more or less racing towards her in order to be polite and service minded (although that's presumably for mistaking her for a tourist instead of an immigrant, letting their politics shine through...).