[NTG-context] export: graphic within table (error)

Hans, I'm getting this error if I put an image within a table using the export backend: ! LuaTeX error /usr/share/texmf/tex/context/base/back-exp.lua:297: bad argument #3 to 'format' (string expected, got boolean). Minimal example: --- \setupbackend[export=yes] \starttext % \externalfigure[mill] % -- fine \bTABLE % \bTR \bTD test \eTD \eTR % -- fine \bTR \bTD \externalfigure[mill] \eTD \eTR % -- error \eTABLE \stoptext --- Log attached. Adam