[Ifeffit] merging data

Hello, I am observing some behavior in (D)Athena that I do not understand, and I was hoping someone could explain it to me. I have attached a project file to illustrate my question. The first two groups in the file have been normalized such that mu(E) and norm(E) are identical. I then merged these groups in mu(E) and norm(E), also in the file. Since mu(E) and norm(E) are the same for the groups, I would expect the data merged in mu(E) and norm(E) to also be identical, but it is not. While it is clear that merging in mu(E) is averaging the groups, it seems merging in norm(E) is not. So what is merging in norm(E) doing? Thank you, George