MailScanner stops working after midnight

The MailScanner installed on our mail server suddenly stopped processing mails after midnight. After having a look at the log I noticed a file permission problem. Directory /var/spool/MailScanner/quarantine was owned by root instead of postfix. Why did the permission change ? Because to test our MailScanner installation I ran the following command MailScanner --lint --debug-sa. Obvisouly this command changed the owner of the directory. It seems to be a bug.