Now I must ask if Anna's entire book is "Soviet disinformation"!
As both an editor and a freelancer I know that words, phrases, and even entire paragraphs can be reworked or omitted entirely. (I could expound on this subject but for now will forbear!!) However--and perhaps I've misread or misunderstood--I have to question the possibility of her autobiography, in which that reference to Derevenko appears, as not being most of her own work. Though she undoubtedly received assistance in writing it, her voice seems consistant throughout the book and the personality portrayed tallies with what Felix, Lili, Isa and others say about her. So I'm hoping, Belochka, that you are not including the book published for English readers with any Russian publication purported to have been written by her.
Also, re: the Derevenko episode, do we know that she remained silent? (I don't have her bio with me at this time.) It's possible she might have complained to Alexandra or someone else and simply not indicated in her book that she did so. Also, the possibility exists that she may have remained silent because of the volatile situation in general. That is, of course, if the incident actually occured, or occured as described. I still think there's a possibility she might have misinterpretted what she saw . . . perhaps have deliberately have misinterpretted the incident so as to score off some sort of grudge.
If I recall correctly, Derevenko had a son about the age of Alexei. So as a parent rather than as a single man, as were several of the tutors, he might be more likely to enforce rules and discipline. (And despite their generally indulgent behavior towards Alexei, Nicholas and Alexandra also may have looked to Derevenko as someone who could keep their son reasonably contained.) It is possible, as I mentioned before, this is the type of episode Anna may have witnessed, and perhaps on more than one occasion, and that she possibly used this sort of observance(s) to jab a pin into Derevenko's reputation for what we would call a "gotcha!"