Hi,

the following example results in a LuaTeX error:

\showboxes
\starttext
  \dorecurse{30}{\footnote{foo}}
\stoptext

! LuaTeX error ...ext-beta/tex/texmf-context/tex/context/base/trac-vis.lua:524: You can't assign a glue_spec node to a prev field

stack traceback:
	[C]: in function '__newindex'
	...ext-beta/tex/texmf-context/tex/context/base/trac-vis.lua:524: in function 'ruledbox'
	...ext-beta/tex/texmf-context/tex/context/base/trac-vis.lua:810: in function 'visualize'


Marco