Once in a while (no pattern AFAICT), I get an email from Zimbra's cron daemon with the subject:-
Cron <zimbra@servername> /opt/zimbra/libexec/zmstatuslog
/opt/zimbra/libexec/zmstatuslog already running with pid xxxxx (differs)
Not quite sure where to start looking, so can't really provide any more info than the above. There doesn't seem to be any issues with the server (ZCS 4.5.10) or anything...