Cannot change font of operators

[d125q]

Description

Using \operator@font followed by something like \mathbb makes causes the symbol not to appear in the output at all. See the corresponding TeX.SE discussion.

My version of unicode-math is:

package:     unicode-math
category:    Package
shortdesc:   Unicode mathematics support for XeTeX and LuaTeX
longdesc:    This package will provide a complete implementation of unicode maths for XeLaTeX and LuaLaTeX. Unicode maths is currently supported by the following fonts: Cambria Math (Microsoft), Minion Math (Johannes Kuster, typoma GmbH) Latin Modern Math (Boguslaw Jackowski, Janusz M. Nowacki) TeX Gyre Pagella Math (Boguslaw Jackowski, Janusz M. Nowacki) Asana-Math fonts (Apostolos Syropolous), Neo Euler (Khaled Hosny), STIX (STI Pub), and XITS Math (Khaled Hosny). As well as running XeTeX or LuaTeX, this package requires recent versions of the fontspec, expl3, xpackages, filehook, ucharcat and lualatex-math packages.
installed:   Yes
revision:    46300
sizes:       src: 269k, doc: 2321k, run: 501k
relocatable: No
cat-version: 0.8k
cat-date:    2018-01-13 15:04:43 +0100
cat-license: lppl1.3c
cat-topics:  maths font-use luatex xetex unicode
collection:  collection-latexrecommended

Minimal example demonstrating the issue

\documentclass{article}

\usepackage{unicode-math}

\begin{document}
\makeatletter
\({\operator@font E}\)
\({\operator@font \mathbb{E}}\)
\makeatother
\end{document}