I've always been a bit concerned about learning other people's mistakes, but this never fully explained why I always feel a bit funny about talking to other learners.

Well, I think I've worked it out.

Last night, I was listening to a German woman talking Italian, and because I didn't have the Italian accent as a cue (she has a strong German accent), my brain didn't switch into Italian mode properly, and it felt like I was listening to Spanish-with-errors instead.

Interesting.