In the future, I will not change the subject so
drastically so that people like yourself will not be
confused.

This isn't a "problem" with the user. It's a function of the software. I use Agent. Even though
you say you clicked on the Reply button, your message with the subject "Never Mind...." appears
as a new thread in my newsreader.

As others have said, you shouldn't change the subject in a situation like this.