When it comes to learning a foreign language, the impediments to becoming fluent aren't only linguistic. They are sometimes cultural. You find that these problems are relatively hard to dislodge, particularly among lower level students. Even when the correction is simple and there is a hard and fast rule they can memorize and follow, they get stuck in conceptualizing a situation in a particular way and forget the rules.
One of the persistent problems I've experienced with this is over whether or not students can or should call me "Mrs. MyLastName". The problem for them is that I'm married but I didn't take my husband's family name. They seem to understand the notion that a married woman may be addressed as "Mrs." and a single one as "Ms." or "Miss." They can't seem to process the idea that I'm married but it's improper to address me as "Mrs."
There are a few reasons for this. One is that the Japanese don't change titles based on gender or marital status. They change them based on status, relationship to the other person, or age. The bigger problem, in my opinion, is that a married person in Japan can't have a different name than his or her spouse. There's a family registry system which requires that a married person choose a family to register with. A wife can register as part of her husband's family and take his name or vice versa for a husband (though the latter is relatively rare, it isn't legally prohibited).
I'm not really all that bothered by being improperly addressed but I do find it peculiar to be addressed in the same manner as my mother would. The main reason to continue to teach the correct way to students is to facilitate some level of cross-cultural understanding on this point.
Of course, I prefer that my students just call me "Shari" and that fixes the entire problem.