There are 12 sites set up in my ISPConfig server. I wanted to change the www host for these from A records to CNAME records in the DNS. Using ISPConfig I deleted the www A records for all 12. Then I emptied the recycle bin. ISPConfig let me add the CNAME record for the first site but for all the others told me there was an existing A record for that name. Nothing in the recycle bin, even rebooting the machine didn't help. I went in with phpMyAdmin and indeed saw A records for the www hosts with the outside world IP addresses, also some A records for an old IP address I don't have anymore. I deleted them all manually. Then going back into ISPConfig I was allowed to put the CNAME records in without problem.