# Error with package diffcoeff

When loading the diffcoeff package, even in very basic examples, I'm getting a repeated error that wasn't there a few weeks ago. Does anyone know what the problem is? Thanks!

Here is the MWE:

\documentclass[letterpaper,12pt]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian,english]{babel}
\usepackage{diffcoeff}
\diffdef {}
{
op-symbol    = \mathrm{d},
op-order-sep = 0 mu
}
\begin{document}

Some text.

\end{document}


And here is the error:

/usr/local/texlive/2022/texmf-dist/tex/latex/diffcoeff/diffcoeff.sty:138:
Illegal parameter number in definition of \key code >
template/derivative/DERIV/long-var-wrap/dv.
2
l.138   }

• I'm working on it Jun 7 at 14:21
• I am discussing with the LaTeX team: the issue arises due to a package change, but that was deliberate and potentially highlights an issue. Jun 7 at 14:34

I couldn't reproduce the error until an xtemplate update this morning. I've amended diffcoeff following a suggestion from Joseph Wright and uploaded the revised version (4.1) to CTAN a few minutes ago.
• I think it was fixed after an update of diffcoeff, are you sure you have the latest version of the package installed? 2 days ago
• Checking my installation of MiKTeX, it hasn't updated diffcoeff yet. (Still has v.4.0 rather than v.4.1.) CTAN has the later version. yesterday