I'm having the same problem.
"man -k <keyword>" doesn't find man pages in
/usr/share/man directories, despite
/usr/share/man being in
/usr/lib/man.conf. I tried
"makewhatis /usr/share/man", and this successfully built a
whatis database in that folder. However,
"apropos" "man -k" and
"echo $MANPATH" still miss
/usr/share/man /usr/lib/man.conf is the only man.conf file on the system that isn't a manpage
for man.conf

Oddly, the
"man -d" command, which is supposed to list the directories searched by man, include /usr/share/man...
root:$ man -d
Reading config file /usr/lib/man.conf
found man directory /usr/man
found man directory /usr/local/man
found man directory /usr/local/share/man
found man directory /usr/share/man
found man directory /usr/X11R6/man
found man directory /opt/postgresql/man
found man directory /opt/seamonkey/man
found manpath map /bin --> /usr/share/man
found manpath map /sbin --> /usr/share/man
found manpath map /usr/bin --> /usr/share/man
found manpath map /usr/sbin --> /usr/share/man
found manpath map /usr/local/bin --> /usr/local/share/man
found manpath map /usr/local/sbin --> /usr/local/share/man
found manpath map /usr/X11R6/bin --> /usr/X11R6/man
found manpath map /usr/bin/X11 --> /usr/X11R6/man
found manpath map /usr/bin/mh --> /usr/share/man
using /usr/bin/less -is as pager
using firefox as browser
using /usr/bin/lynx -dump to dump HTML pages as textWhat manual page do you want?