Remapping fonts in unicode-math has no effect on e.g. `\mscrC`

Question

For some reason, in this setup, \mathscr{C} and \mscrC produce different results:

\documentclass[12pt,a4paper]{article}
\usepackage{unicode-math}
\unimathsetup{math-style=TeX} 
\setmathfont{Cambria Math}
\setmathfont[range={\mathscr,\mathbfscr},StylisticSet=0]{xits-math.otf}
\begin{document}
\[
\mathscr{C}, \mscrC
\]
\end{document}

In the result, \mathscr{C} respects the remapping, but \mscrC does not. I was under the impression that unicode-math translates the former to the latter, but it seems as if \mathscr here contains some additional processing that "knows" about fonts. A literal 𝒞 behaves like \mscrC. The only thing that seems to work is redefining \mscrC after \begin{document} to force it to go through \mathscr.

1. What is unicode-math really doing?

2. How do I work around this?

Answer 1

I'm not sure but I think that it is not a bug but a feature: It gives you the possibility to use different fonts even if the "destination position" is the same. \mathscr{C}, \mscrC and also \mathcal{C} all print the char "1D49E. The current behaviour means that e.g. \mathscr and \mathcal can come from different fonts:

\documentclass[12pt,a4paper]{article}
\usepackage{unicode-math}

\unimathsetup{math-style=TeX}
\setmathfont{Cambria Math}
\setmathfont[range={\mscrC,\mathscr,\mathbfscr},]{xits-math.otf}

\begin{document}
\mscrC
\[
\mathscr{C}, \mscrC,\mathcal{C}
\]
\end{document}

If you want to change the look of \mathcal too you will have to add it to the list too (like I did for \mscrC).