I just noticed hat as dasd.4 is a new man page, and ed.4 is a link to it,
there is an ordering problem, as the link is created before the file it
references exists. ie.,

  ln -f ../dasd.4 ed.4

happens before

  install -r -p -c   -o root -g wheel -m 444 /usr/src/share/man/man4/dasd.4
/usr/share/man/man4/dasd.4

In bsd.man.mk we essentially have

maninstall:	manlinks
...
manlinks:	manpages

Does that want an extra target

maninstall:	manlinks	# overall target
manlinks:	MANINSTALL	# makes links on installed manpages
MANINSTALL:	manpages	# installs manpages

?

Cheers,

Patrick