If a parent asked you what you meant by challenging and you started rhyming off a list : well lets see he put the truck on the shelf when I asked him to put it by the closet and then the one of the little ones came around the corner and tripped on it which is why I insist the trucks go on the shelf, I called him for lunch and he said just a minute but then got upset because I went ahead and served everyone else and then got upset because he was the last one to finish eating so the last one to move onto to the next course of food, he didnt' want to listen to the story I had chosen for the day and wanted his choice which I promised to read after naptime when we did storytime again but for this morning we needed to read the story that went with the theme for the week, .......I think you get my drift here. Yes the poor caregiver was being accosted at every stage of the day. Nothing major just annoying stuff. With time the child will learn the routine and what to expect when and problem will be solved but till then every time this child opens his mouth to say something it is going to be taken the wrong way since three year olds don't phrase their intentions tactfully most of the time.
There is also something to be said for letting the child fight his own battles so while he needs to know that mom will support him he also needs to learn that she will support the caregiver too and not reward him for misbehaviour. Three year olds can be very outspoken and cheeky and do not like it when we refuse to be spoken to in that way. Just be careful you are not encouraging this kind of independent thinking and talking at home without teaching him that there is a time and place for that and a time and place for acceptance/obedience/remembering his place in the people chain.