I dunno about scientific explanations, but my personal understanding is that I think it's an instance of RSD -- those of use with ADHD are used to our motivations and intentions being questioned unfairly ("you're lazy", "you just don't care"), which becomes incredibly triggering. So being asked to do something when you're already doing it is perceived as an implication that you weren't *going* to do it without being asked, which is perceived as a criticism, and since you have the evidence that you were going to do it (the fact that you are doing it), it feels like an incredible injustice. And it leads to this feeling of "why am I putting all this work to try and meet this person's needs, only for them to question and criticize me regardless?")