Unexpected images order with ConTeXt startcombination

Question

I want to use combinations to show a chronological overview of the Eastern Roman Empire at different ages. The trouble is my pictures are displayed in a apparently random order.

\defineexternalfigure[carte][width=0.45 \textwidth ]

\starttext    
\placefigure[here][fig:cartes]
   {Extension de l’Empire romain d’Orient à différentes dates. Droits d’auteurs :}
   {\startcombination[2*4]
      {\externalfigure[./illustrations/cartes-empire-romain-orient-0.png][carte]}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-1.png][carte]}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-2.png][carte]}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-3.png][carte]}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-4.png][carte]}
%      {\externalfigure[./illustrations/cartes-empire-romain-orient-5.png][carte]}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-6.png][carte]}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-7.png][carte]}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-8.png][carte]}
   \stopcombination}   
\stoptext

I would expect some

| 0 | 1 |

| 2 | 3 |

| 4 | 6 |

| 7 | 8 |

Here is what I get (pay attention to the numbers).

The wider line between row 2 and 3 may be a clue. Did I miss something?

Answer 1

I luckily found the issue while adding titles for each picture (something I didn't plan at first). The next externalfigures where taken as title, hence the wider line and unexpected order. If I add empty titles, everything goes as expected.

\defineexternalfigure[carte][width=0.45 \textwidth ]

\starttext

\placefigure[fig:cartes]
   {Extension de l’Empire romain d’Orient à différentes dates. Droits d’auteurs :}
   {\startcombination[2*4]
      {\externalfigure[./illustrations/cartes-empire-romain-orient-0.png][carte]}{}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-1.png][carte]}{}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-2.png][carte]}{}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-3.png][carte]}{}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-4.png][carte]}{}
%      {\externalfigure[./illustrations/cartes-empire-romain-orient-5.png][carte]}{}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-6.png][carte]}{}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-7.png][carte]}{}
      {\externalfigure[./illustrations/cartes-empire-romain-orient-8.png][carte]}{}
   \stopcombination}

\stoptext

ConTeXt wiki info may be outdated, because it stats that we can bypass the empty caption. I shall update it ASAP.