It seems that "horde" has duplicate entries.
After looking in /etc/logrotate.d/ I found that both the "bubba-horde" and "horde3" tries to rotate the same log-files. I guess that this is no big issue, removing one of the entries should do the suffice.
Worse is, however, that the horde log doesn't want to be rotated.
Forcing a rotate, executing "logrotate -d -f bubba-horde", prints:
...
copying /var/log/horde/horde3.log to /var/log/horde/horde3.log.1
truncating /var/log/horde/horde3.log
error: unable to open /var/log/horde/horde3.log.1 for compression"