How to respond to a professor who was insulted by an email detailing mistakes in the exercise? I am an undergraduate student. Preparing the solution to an exercise regarding computer assembly language programming I discovered an error in the program skeleton that was given to us to base our solution on (one of the instructions was illegal, because its immediate operand was outside the permitted range).

I sent an email to the professor's address for "questions and clarifications" regarding the exercise, explaining in detail (about 5 paragraphs) and citing a textbook, why the skeleton program would not compile (assemble) and finally commenting that it seems surprising that this error would make it to the question text, since simply running the assembler on the skeleton program would reveal it.

I got the reply that indeed there was an error in the program skeleton but it was put there on purpose and one of the objectives of the exercise was to see if we (students) would spot it and correct it.

There was no mention of this in the question text. The exact wording of the question text was "complete the program below so that it performs the desired function".

Now the professor wants me to apologize because my comment implied that there was carelessness on their part. I am not convinced about their answer, and worse, even if I were convinced, I believe deliberately misleading the student to be worse than simply being careless. I cannot give an honest apology. What should I reply, if anything?
To me, this is such a non-issue that it doesn't warrant much of a response. So let me add a response :)


  I didn't mean to imply carelessness, and I am sorry if that's how my email came across. I was a bit overzealous in my email. I will address the errors in the skeleton program in my solution, as you have indicated. Thank you for your detailed response!


I think you should take this (very minor) “incident” as a learning experience about how people might perceive your communications. Professors are people; they sometimes make mistakes, they sometimes make pedagogical choices that students don't agree with, and they all take criticism differently.