Mark as broken with recent texinfo:
makeinfo -I ./doc -I . --html --no-split ./doc/ztcl.texi -o ztcl.html
./doc/ztcl.texi:366: raising the section level of @subsection which is too low
./doc/ztcl.texi:990: raising the section level of @unnumberedsubsubsec which is too low