[$] Unexpected fallout from /usr merge in Debian

Back in 2011, Harald Hoyer and Kay Sievers came up with a proposal for
Fedora
to
merge much of the operating system into /usr; former top-level
directories, /bin, /lib,
and /sbin, would then become symbolic links pointing into the
corresponding subdirectories of /usr.
Left out of the merge would be things like
configuration files in /etc, data in
/var, and user home directories. This change was aimed at
features like atomic upgrades and easy snapshots. The switch
to a merged /usr was successful for Fedora 17; many other
distributions (Arch,
OpenSUSE, Mageia,
just to name a few) have followed suit. More recently, Debian has been
working toward a merged /usr, but it ran into some surprising
problems that are unique to the distribution.