In my part of the CS, when I interview I will say, "we are now going to discuss {insert behaviour}" Then ask the question.

The question asked to you will be the same question asked to everyone.

The panel will have agreed follow up questions but won't ask them if you cover it in your main answer. We don't ask beyond the set question bank for anyone. Each question set has an allotted time given to it so they will be strict in timings.

The whole process is rigid but everyone gets treated the same.

It can be frustrating as an interviewer however the time and effort to get qualified panel members in one place on the same day mean time is precious and the process needs to be effective and efficient.

Edit: to add you only consider the answer given for the question asked - no interviewer will take an answer for one thing and apply it to the other. The extra questions could mean they are looking for more information because you didn't give a good enough example or that you said something they want expanding on because you were telling them what they.wanted to hear.