Medium cmss substituted for bold: collateral damage or bug? (Not sure if expected or not)

[cfr42]

If the current series is b and the default sans is neither cmss nor lmss, an attempt to switch to cmss causes medium to be substituted. Thereafter, all bold cmss uses the medium, unless bx is explicitly requested.

This happens because the font definition file ot1cmss.fd does not declare a substitution for b. While it never did, the current series is much more likely to be b for post-2020 LaTeX, while the series change rules do not apply (at the right point).

MWE

\RequirePackage{latexbug}
\documentclass{article}
% because latexbug complains about wiser choices
\usepackage{times}
\begin{document}
\makeatletter
{\bfseries\fontfamily{cmss}\selectfont\curr@fontshape\par}
{\fontfamily{cmss}\bfseries\selectfont\curr@fontshape\par}
\makeatother
\end{document}

Log file attached below, but I suppose 2 lines are sufficient:

LaTeX Font Warning: Font shape `OT1/cmss/b/n' undefined
(Font)              using `OT1/cmss/m/n' instead on input line 7.

Also applies to at least T1, TS1 and U.

Including suitable substitutions in ot1cmss.fd, t1cmss.fd, ts1cmss.fd and ucmss.fd would arguably be more backwards compatible than the status quo with pre-2020 LaTeX, as well as less confusing for users. But it would obviously be less backwards compatible with 2020-2024 LaTeX and perhaps have negative consequences besides.

Att.: prawf-2.log

Related: https://tex.stackexchange.com/q/735923/

[cfr42]

Related: #277

[cfr42]

TL 2019 log for comparison:

log.log