Hi Bernard,

Transposing your table to an example given by Wolfgang Schuster some time ago I obtain the correct behavior, but I don’t know where the problem in your example comes from…

Please see whether the following gives what you want and comapre with the PDF I get here with ConTeXt  version 2018.01.14 15:55.

Best regards: OK

%%%% begin caption-numberstopper-0.tex
\setupexternalfigure[location=default]

\setupcaptions[numberstopper={:}]
\starttext

Take a look at \at{picture}[fig:cow] below.

\startplacefigure[reference=fig:cow,title=A dutch cow]
 \externalfigure[cow]
\stopplacefigure

\placefigure[here][photo]{This is a cow}{\externalfigure[cow][width=2in]}

Take a look at \at{table}[tab:1] below.

\placetable[here][tab:1]{This is a table}{
\starttable[|c|c|]
\HL
\NC \bf Year \NC \bf Number of ships \NC\SR
\HL
\NC 1645 \NC 450 \NC\FR
\NC 1671 \NC 480 \NC\MR
\NC 1676 \NC 500 \NC\MR
\NC 1695 \NC 930 \NC\LR
\HL
\stoptable}

\stoptext
%%%% end caption-numberstopper-0.tex