It seems, that
\setupfloats[indentnext=yes]
has nothing to do with indenting of next paragraph.
What is the real meaning of this option?
indentnext=yes is indeed related to indentation. Search for threads
"[NTG-context] Indentation bug ?" and "[NTG-context] Indentation bug ?
Sample"...
\indentation is the solution (Thanks to David) or you can cheat by
placing \placefigure or \placefloat before \section os \subsection...
when they use page, top, bottom, auto or page...