\setupcolors[state=start]
\setuppagenumber[state=stop]

\pdfcompresslevel=0
\pdfobjcompresslevel=0

\startuniqueMPgraphic{FOO}
    fill OverlayBox withcolor lightgray;
\stopuniqueMPgraphic

\defineoverlay[FOO][\uniqueMPgraphic{FOO}]
\definelayer[BAR]



\starttext

% OK
\setlayer[BAR][x=0mm,y=0mm]
{\framed[background=color,backgroundcolor=lightgray,frame=off]
{\startoverprint first one\stopoverprint}}
\setlayer[BAR][x=50mm,y=0mm]
{\framed[background=color,backgroundcolor=lightgray,frame=off]
{\startoverprint second one\stopoverprint}}

% OK
\setlayer[BAR][x=0mm,y=15mm]
{\framed[background=color,backgroundcolor=lightgray,frame=on]
{\startoverprint first one\stopoverprint}}
\setlayer[BAR][x=50mm,y=15mm]
{\framed[background=color,backgroundcolor=lightgray,frame=on]
{\startoverprint second one\stopoverprint}}

% OK
\setlayer[BAR][x=0mm,y=30mm]
{\framed[background=FOO,frame=on]
{\startoverprint first one\stopoverprint}}
\setlayer[BAR][x=50mm,y=30mm]
{\framed[background=FOO,frame=on]
{\startoverprint second one\stopoverprint}}

% ( layer + overlay + frame=off ) is buggy
\setlayer[BAR][x=0mm,y=45mm]
{\framed[background=FOO,frame=off]
{\startoverprint first one\stopoverprint}}
\setlayer[BAR][x=50mm,y=45mm]
{\framed[background=FOO,frame=off]
{\startoverprint second one\stopoverprint}}


\flushlayer[BAR]

\stoptext