during today's update from calibre 0.9.14-1 -> 0.9.15-1, pacman complained that all packages under /usr/lib/calibre/calibre were already existing in the filesystem, and therefore the update couldn't be performed. for some reason "pacman -Qo" claimed that all these files didn't belong to any package. only after moving them from that location somewhere else could the new version of calibre be installed. looks to me as if this is some packaging error. don't know enough about arch packaging though to say what exactly went wrong... -- phani.
