It seems to be related to this thread on the ArchLinux wiki, titled: [journalctl issues][1]. It seems to have something to do with this setting `SystemMaxUse` in /etc/systemd/journald.conf. 

The thread isn't conclusive but several people were having some luck in either clearing out the logs under `/var/log/journal/*` or increasing the value for `SystemMaxUse`.


  [1]: https://bbs.archlinux.org/viewtopic.php?id=153922