In a primary DNS zone file I've made a manual entry below the line saying ";;;; MAKE MANUAL ENTRIES BELOW THIS LINE! ;;;; and it gets modified when the file is rewritten after making a change to the zone in the web interface. The change is that it strips leading whitespace from lines in the manual entries section. The problem is that the line I have in that section is a third NS record (because ISPConfig only allows entry of two), and if that leading whitespace is stripped out, the whole zone then fails to load when bind is restarted - and I find out about it about a week later when all my hosts suddenly stop resolving as the backup nameservers time out. Fix required: Make sure the manual entries section is preserved utterly verbatim, do not even strip leading whitespace from lines.