Sorry for bad vocabulary (not time to check e.g. TeX by Topic for exact one).
This fails with current master at 9461aa1fdf4
\documentclass{article}
\usepackage{unravel}
\begin{document}
% raises error
\unravel{\dimen255=3\catcode`\p\relax}
% this is ok
\dimen255=3\catcode`\p\relax
\number\dimen255 % 33 = 3 times 11
\end{document}
Sorry for bad vocabulary (not time to check e.g. TeX by Topic for exact one).
This fails with current master at 9461aa1fdf4
I have inserted the
\relax
only for extra safety.