autoSectionLabels error: sec prefix missing

[sdknij]

I have made a simple test in markdown:

# Headline A
## Headline B
## Headline C {#sec:section1}
# Headline D
## Headline B
## Headline C {#section2}

When running pandoc with pandoc-crossref and autoSectionLabels I get the following:

\section{Headline A}\label{headline-a}
\subsection{Headline B}\label{headline-b}
\subsection{Headline C}\label{sec:section1}
\section{Headline D}\label{headline-d}
\subsection{Headline B}\label{headline-b-1} 
\subsection{Headline C}\label{section2}

The manual set label (section1) works using @sec:section1. But the automated label seems missing the sec: prefix. Or have I misunderstood something?