Segmentation code ignored when a tcolorbox breaks

Question

Consider the following mwe:

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{skins,breakable}
\usetikzlibrary{calc}
\usepackage{lipsum}
\begin{document}
   \begin{tcolorbox}[enhanced,breakable,segmentation code={\draw[red]($(segmentation.west)+(1,0)$)--($(segmentation.east)+(-1,0)$);}]
    test
    \tcblower
    Works as expected
   \end{tcolorbox}

    \begin{tcolorbox}[enhanced,breakable,segmentation code={\draw[red]($(segmentation.west)+(1,0)$)--($(segmentation.east)+(-1,0)$);}]
    \lipsum
    \tcblower
    Does not work as expected
   \end{tcolorbox}
\end{document}

Unbroken box result:

Broken box result:

The goal is to have a tcolorbox with the given segmentation style, e.g. a red line a bit shorter than the box width.

The code works fine if the box does not break, but it seems to be ignored when the box breaks. What am I doing wrong?

Edit: I just discovered than I can force the segmentation code after the break putting it inside a extend freelance last, but this is not a viable solution since it also changes the appearance of the frame in an undesired way.

Answer 1

For tcolorbox versions prior to 3.00 (2014/05/08), if you want to use segmentation code you need the freelance key instead of enhanced (in fact, with your original settings, your code doesn't produce the image you showed in the question; the segmentation code option is ignored on both cases if enhanced is used and not freelance):

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{skins,breakable}
\usetikzlibrary{calc}
\usepackage{lipsum}
\begin{document}
   \begin{tcolorbox}[freelance,breakable,segmentation code={\draw[red]($(segmentation.west)+(1,0)$)--($(segmentation.east)+(-1,0)$);}]
    test
    \tcblower
    Works as expected
   \end{tcolorbox}

    \begin{tcolorbox}[freelance,breakable,segmentation code={\draw[red]($(segmentation.west)+(1,0)$)--($(segmentation.east)+(-1,0)$);}]
    \lipsum
    \tcblower
    Works as expected
   \end{tcolorbox}
\end{document}

However, using the freelance skin changes the way the box behaves at page breaks, so you would need to redo some parts of the box to get the original behaviour.

Starting from tcolorbox 3.00 (2014/05/08), segmentation code can also be used with enhanced, but I'd suggest using segmentation style instead of segmentation code (this will work in all versions):

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{skins,breakable}
\usetikzlibrary{calc}
\usepackage{lipsum}

\newtcolorbox{mybox}{
  enhanced,
  breakable,
  segmentation style={red,solid,shorten >= 1cm,shorten <= 1cm}
}

\begin{document}
   \begin{mybox}
    test
    \tcblower
    Works as expected
   \end{mybox}

    \begin{mybox}
    \lipsum
    \tcblower
    Works as expected
   \end{mybox}

\end{document}