less option "--save-marks" does nothing when less is used as a manual pager

I use less version 590 (GNU regular expressions). I use export LESSFILE="/root/.lesshst_for_manpages" export MANPAGER="pager --save-marks -I" man -L en > ... but --save-marks appears to have no effect when setting marks in manuals (using the m command in the pager). When reading the same manual again, the pager does not seem to remember the previously set marks. What can I do?