Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

If the auth responds very slowly and the records expire in between, the capping of TTLs is not enforced for lack of data. This does not happen on regular resolve as then then the 
child records are used immediately if not expired and thus valid, or the
 records are expired, and in that case not used.  So this case 
can only happen if almost expired records are used to refresh the 
authoritative NS records.