I will notice that the person who reported the issue (the last time it was reported anyway

)
reported it on calibre v2.5 -- the same version you were on.
For the future, see my -- Sticky:
Fully automatic calibre installer/updater for linux
Includes a calibre-upgrade.sh (run with sudo to manually upgrade calibre) and a systemd service (if you have a different init, it will instead install a cron job).