I was able to bypass error with

\startluacode
function metapost.free_boxes()
 local tb = tex.box
 init = metapost.first_box or 0
 tini = metapost.last_box or 0
     --for i = metapost.first_box,metapost.last_box do
     for i = init,tini do
         local b = tb[i]
         if b then
             tb[i] = nil -- no node.flush_list(b) needed, else double free error
         else
             break
         end
     end
end
\stopluacode

just after
%context --ctx=t-openoffice Attempt.odt
of t-openoffice.tex