Yes, this was broken in zentyal, then fixed for a while, and now it appears to be broken again. The problem is the config file /etc/logrotate.d/clamav-daemon has been mangled. What I did to fix was:
* Change the first line to be "/var/log/clamav/clamav.log {"
* Change the create line to be "create 640 clamav clamav"
I also changed the create line in /etc/logrotate.d/clamav-freshclam to match