Given that the OP has posted to say that it was a mistake and hence isn't "unmarked" as you put it, you've quite missed the point. Not all mistakes (and corrections) are evidence of some classist plot.
On the contrary, I believe you missed my point! My issue wasn't with the correction; my issue was with the use of the term "poor grammar". I do not believe it is acceptable to use that term in any context, because it has a specific history and connotation.
