[emile]

So to get the problem straight, the students use a grammatically correct response which doesn't sound natural.

I would say this wouldn't be a problem for students in Japan where they would have limited interactions with people in English, probably in very formal situations when they start work. However, if they live in an English-speaking country, it may stop them from making friends and so on if they don't sound natural.

The issue is also that some of the first things people learn when they start learning English, stick for the longest time. Mistakes that people make when they start, like China students saying 'I live in Channa' or 'the eye-nternet' (anyone heard these?) are the toughest to erase.