I have a broken flow cell connection in this minimal example. The broken flow cell is only triggered when drawn within a subsection with an overlay. The logic to create the underlined subsection is by the way copied from the metafun manual source. I do not have the slightest clue what is going wrong in this example. Thanks for ideas.

Best, Bernd

\usemodule[chart]

\startuniqueMPgraphic{SectionUnderline}
   path p;
   p:= unitsquare xscaled OverlayWidth yscaled OverlayHeight;
   draw llcorner p -- lrcorner p;
   setbounds currentpicture to p;
 \stopuniqueMPgraphic

\defineoverlay[SectionUnderline][\uniqueMPgraphic{SectionUnderline}]

\starttexdefinition unexpanded ChapterCommand #1#2
  \framed [background=SectionUnderline] {#2}
\stoptexdefinition

\setuphead
  [subsection]
  [command=\ChapterCommand]

\starttext

\subsection[title=Introduction]

\startFLOWchart[toolchain]

\startFLOWcell
  \location{1,1}
  \connection [bt] {compiler}
\stopFLOWcell

\startFLOWcell
  \name {compiler}
  \location{1,2}
  \shape{product}
\stopFLOWcell
\stopFLOWchart

\FLOWchart[toolchain]
\stoptext