Comment 1 for bug 886705

That base attribute valueof the <book> tag in the .devhelp2 file is apparently set during make install (but only in the copy that is installed, not the original) by this line of the (generated) Makefile:

  devhelp_install = $(doc_install_cmd) --book-base='$(htmlrefdir:/=)'

For instance, you will see these lines during make install

  /bin/mkdir -p '/opt/gnome/share/devhelp/books/gtkmm-3.0'
  /usr/bin/perl -- "../docs/doc-install.pl" --verbose --mode=0644 --book-base='/opt/gnome/share/doc/gtkmm-3.0/reference /html' -t '/opt/gnome/share/devhelp/books/gtkmm-3.0' -- reference/gtkmm-3.0.devhelp2
  doc-install: Using base path /opt/gnome/share/doc/gtkmm-3.0/reference/html for Devhelp book
  doc-install: Translating gtkmm-3.0.devhelp2 (rewrote base path)

(That doc-install perl script is from mm-common.)

That htmlrefdir is based on the standard datarootdir variable. Presumably the debian package passes --datarootdir to configure to change the default, though I don't see where that is done here:
  http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/oneiric/gtkmm3.0/oneiric/files/head:/debian/
That htmlrefdir is apparently also used when installing the .html files, so I wonder how the two locations could get out of sync.

Maybe they use a patch, because I don't see how else you could change gtkmm-3.0 to libgtkmm-3.0 in the $(book_name) here:
  libdocdir = $(datarootdir)/doc/$(book_name)
  referencedir = $(libdocdir)/reference
  htmlrefdir = $(referencedir)/html

It feels like a debian/Ubuntu packageing bug but I'd welcome a patch for upstream gtkmm if it turns out that we are not really doing what the debian/Ubuntu package asks us to do.