SX: subfigure caption format differs for \captionof

Migrated from https://sourceforge.net/p/latex-caption/tickets/44/

From https://tex.stackexchange.com/questions/310330/subfigure-caption-format-differs-for-captionof

When I place a subfigure caption using \captionof, the format differs from the one appearing when placed via \caption inside a subfigure environment.

I suppose this is a bug in the \captionof command? Trying to force it via \captionsetup doesn't work either.

\documentclass{article}
\usepackage{subcaption}

\begin{document}

\begin{figure}
    \begin{subfigure}{\textwidth}
        \caption{A}
    \end{subfigure}
\end{figure}

\captionsetup[sub]{labelformat=parens}
\captionof{subfigure}{B}

\end{document}

changed the description

\captionof{subfigure} should result in an error and not in weird behaviour.

changed title from subfigure caption format differs for \captionof to SX: subfigure caption format differs for \captionof

closed via commit ef16bc39

added Bug2 label

mentioned in commit ef16bc39